Apparatus and methods for individual addressing and noise reduction in actuator arrays

ABSTRACT

Apparatus for generating a target physical effect, at least one attribute of which corresponds to at least one characteristic of a digital input signal sampled periodically, the apparatus comprising a multiplicity of electrostatic actuator elements, each comprising a moving element moving between first and second electrodes, the multiplicity of electrostatic actuator elements including Nr first subsets (R-subsets) of actuator elements and Nc second subsets (C-subsets) of actuator elements, wherein a first partitioning of the multiplicity of actuator elements yields the Nr first subsets (R-subsets) and a second partitioning of the multiplicity of actuator elements yields the Nc second subsets (C-subsets); a first plurality of Nr electrical connections (R-wires) interconnecting the moving elements of actuator elements in each R-subset, such that the moving element of any actuator element in each individual R-subset is electrically connected to the moving elements of all other actuator elements in the individual R-subset, and electrically isolated from the moving elements of all actuator elements not in the individual R-subset; a second plurality of Nc electrical connections (A-wires) interconnecting the first electrodes of actuator elements in each C-subset, such that the first electrode of any actuator element in each individual C-subset is electrically connected to the first electrode of all other actuator elements in the individual C-subset, and electrically isolated from all actuator elements not in the individual C-subset; a third plurality of Nc electrical connections (B-wires) interconnecting the second electrodes of actuator elements in each C-subset, such that the second electrode of any actuator element in each individual C-subset is electrically connected to the second electrode of all other actuator elements in the individual C-subset, and electrically isolated from all actuator elements not in the individual C-subset; and a controller electrically connected to the first, second and third pluralities of electrical connections, operative to receive a digital input signal, and to apply one of a predetermined, finite set of electric potentials to each of said electrical connections respectively, such that resulting movements of the moving elements together produce the desired physical effect.

REFERENCE TO APPLICATIONS

Priority is claimed from U.S. provisional applications No. 61/468,916,entitled “Apparatus and methods for individual addressing and noisereduction in actuator arrays” and filed Mar. 29, 2011 and No. 61/417,298entitled: “Methods for Individual Addressing and Noise Reduction inActuator Arrays” filed on Nov. 26, 2010.

Applications also include the following:

Country Ser. No. Title USA 60/802,126 AN APPARATUS FOR GENERATINGPRESSURE USA 60/907,450 APPARATUS FOR GENERATING PRESSURE AND METHODS OFMANUFACTURE THEREOF USA 60/872,488 VOLUME CONTROL PCT PCT/IL2007/000622APPARATUS AND METHODS FOR GENERATING PRESSURE WAVES USA 60/924,203APPARATUS AND METHODS FOR GENERATING PRESSURE WAVES USA IMPROVEDMANUFACTURING PCT PCT/IL2007/000618 DIRECT DIGITAL SPEAKER APPARATUSHAVING A DESIRED DIRECTIVITY PATTERN PCT PCT/IL2007/000621 VOLUME ANDTONE CONTROL IN DIRECT DIGITAL SPEAKERS USA 60/996,513 IMPROVED SPEAKERAPPARATUS AND METHODS USEFUL IN CONJUNCTION THEREWITH USA 61/136,778ACTUATOR APPARATUS WITH COMB-DRIVE COMPONENT AND METHODS USEFUL FORMANUFACTURING AND OPERATING SAME PCT PCT/IL2009/000943 ACTUATORAPPARATUS WITH COMB-DRIVE COMPONENT AND METHODS USEFUL FOR MANUFACTURINGAND OPERATING SAME USA 61/171,946 DUST PROTECTION APPARATUS FOR FLATDIGITAL LOUDSPEAKERS USA 61/476,352 CORONA DISCHARGE USA 12/301,954VOLUME AND TONE CONTROL IN DIRECT DIGITAL SPEAKERS PCT PCT/IL2008/001524DIGITAL SPEAKER APPARATUS USA 12/301,951 APPARATUS AND METHODS FORGENERATING PRESSURE WAVES USA 12/601,427 DIRECT DIGITAL SPEAKERAPPARATUS HAVING A DESIRED DIRECTIVITY PATTERN

FIELD OF THE INVENTION

The present invention relates generally to actuator arrays and moreparticularly to digital loudspeakers.

BACKGROUND OF THE INVENTION

Conventional technology pertaining to certain embodiments of the presentinvention is described in the following publications inter alia:

Apparatus and methods for generating pressure waves are known e.g. fromco-pending published PCT application WO 2007/135680; digital speakerdevices are known e.g. from co-pending published PCT application WO2009/066290.

Conventional noise shaping also termed sigma-delta modulation anddelta-sigma modulation is described in “Understanding Delta-Sigma DataConverters” by Richard Schreier and Gabor C. Temes.

The disclosures of all publications and patent documents mentioned inthe specification, and of the publications and patent documents citedtherein directly or indirectly, are hereby incorporated by reference.

SUMMARY OF THE INVENTION

The presently disclosed subject matter includes methods and apparatusfor generating a physical effect using a multiplicity of electrostaticactuator elements (actuator array) wherein each actuator elementincludes a first electrode, a second electrode and a moving element,e.g. as described herein with reference to FIGS. 1A-1C, and whereinsubsets of first electrodes, subsets of second electrodes, and subsetsof moving elements, are electrically interconnected, e.g. as describedherein with reference to FIGS. 2 and 3.

Certain aspects of the presently disclosed subject matter are “driveschemes”, i.e. methods and apparatus for causing movement of one or moreselected moving elements while preventing movement of other (unselected)moving elements, by applying one of a finite, predetermined set ofvoltages to each electrically interconnected subset of first electrodes,to each electrically interconnected subset of second electrodes, and toeach electrically interconnected subset moving elements. According tosome aspects of the present invention, the number of different drivevoltages employed by a drive scheme, and/or their magnitude, areminimized, thus facilitating cost-effective implementation of theapparatus. According to further aspects of the present invention, thenumber of opportunities per time unit for initiating movements of movingelements is increased, thus increasing the time resolution of theapparatus, facilitating more accurate generation of the desired physicaleffect.

A further aspect of the presently disclosed subject matter is“initialization”, i.e. a method for bringing all moving elements withinthe actuator array into a known, useful starting position, using onlythe drive voltages already employed by a drive scheme (i.e. withoutrequiring additional voltages), e.g. as shown in FIG. 13.

According to still further aspects of the presently disclosed subjectmatter, an apparatus, e.g. as shown in FIG. 14, including an actuatorarray and a controller, operates as a type of digital-to-analogconverter whose analog output is a physical effect such as, for example,audible sound. The controller may apply drive voltages to eachelectrically interconnected subset of first electrodes, to eachelectrically interconnected subset of second electrodes, and to eachelectrically interconnected subset moving elements synchronously with anactuation clock, whose frequency may differ from the frequency at whicha digital input signal to the controller is sampled.

Further aspects of the presently disclosed subject matter are “elementselection methods”, i.e. methods for bringing the number of movingelements in a particular position or moving in a particular directionduring each cycle of an actuation clock, sufficiently close to a desiredvalue to enable accurate production of a desired physical effect, e.g.as shown in FIGS. 15 to 23.

Still further aspects of the presently disclosed subject matter aremethods for shaping the frequency spectrum of different types of noisewhich may occur in the physical effect produced, including: mismatchnoise resulting from differences in the magnitude of the physical effectproduced by each actuator element, addressing noise resulting from theinability of element selection methods under certain conditions to makethe number of moving elements in a particular position or moving in aparticular direction exactly equal to a desired value, and quantizationnoise resulting from the number of actuator elements in said actuatorarray being less than the number of possible values a digital inputsignal can assume.

It is appreciated that any or all of the computational steps shown anddescribed herein may be implemented as dedicated electronic circuits,such as for example, in an application specific integrated circuit(ASIC), or using reconfigurable circuits, such as for example, a fieldprogrammable gate array (FPGA), or may be implemented in softwarerunning on, for example, a microcontroller, digital signal processor(DSP), or other type of microprocessor.

The above devices may communicate via any conventional wired or wirelessdigital communication means, e.g. via a wired or cellular telephonenetwork or a computer network such as the Internet.

The apparatus of the present invention may include, according to certainembodiments of the invention, machine readable memory containing orotherwise storing a program of instructions which, when executed by themachine, implements some or all of the apparatus, methods, features andfunctionalities of the invention shown and described herein.Alternatively or in addition, the apparatus of the present invention mayinclude, according to certain embodiments of the invention, a program asabove which may be written in any conventional programming language, andoptionally a machine for executing the program such as but not limitedto a general purpose computer which may optionally be configured oractivated in accordance with the teachings of the present invention. Anyof the teachings incorporated herein may wherever suitable operate onsignals representative of physical objects or substances.

The embodiments referred to above, and other embodiments, are describedin detail in the next section.

Any trademark occurring in the text or drawings is the property of itsowner and occurs herein merely to explain or illustrate one example ofhow an embodiment of the invention may be implemented.

Unless specifically stated otherwise, as apparent from the followingdiscussions, it is appreciated that throughout the specificationdiscussions, utilizing terms such as, “processing”, “computing”,“estimating”, “selecting”, “ranking”, “grading”, “calculating”,“determining”, “generating”, “reassessing”, “classifying”, “generating”,“producing”, “stereo-matching”, “registering”, “detecting”,“associating”, “superimposing”, “obtaining” or the like, refer to theaction and/or processes of a computer or computing system, or processoror similar electronic computing device, that manipulate and/or transformdata represented as physical, such as electronic, quantities within thecomputing system's registers and/or memories, into other data similarlyrepresented as physical quantities within the computing system'smemories, registers or other such information storage, transmission ordisplay devices. The term “computer” should be broadly construed tocover any kind of electronic device with data processing capabilities,including, by way of non-limiting example, personal computers, servers,computing system, communication devices, processors (e.g. digital signalprocessor (DSP), microcontrollers, field programmable gate array (FPGA),application specific integrated circuit (ASIC), etc.) and otherelectronic computing devices.

Elements separately listed herein need not be distinct components andalternatively may be the same structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the present invention are illustrated in thefollowing drawings:

FIGS. 1A to 1C are cross-sectional illustrations of one type ofdouble-sided electrostatic actuator element useful in forming actuatorarrays in accordance with certain embodiments of the invention.

FIGS. 2-4 are simplified schematic diagrams of actuator arrays inaccordance with certain embodiments of the invention.

FIGS. 5-7 illustrate drive schemes according to which various actuatorarrays may operate, all in accordance with certain embodiments of theinvention.

FIGS. 8, 11 and 12 are tables useful in understanding certainembodiments of the invention.

FIGS. 9 and 13 are graphs useful in understanding certain embodiments ofthe invention.

FIG. 10 is a simplified representation of an actuator array constructedand operative in accordance with certain embodiments of the invention.

FIG. 14 is a simplified block diagram of a controller and actuator arraycontrolled thereby, constructed and operative in accordance with certainembodiments of the invention.

FIGS. 15 to 23 are simplified flowchart illustrations of processestogether forming an element selection method, operative in accordancewith certain embodiments of the invention.

FIGS. 24-26 are simplified representation of an actuator array invarious positions, e.g. after a swapping procedure, all in accordancewith certain embodiments of the invention

FIGS. 27-29 are simplified block diagrams of a controller and actuatorarray controlled thereby, all constructed and operative in accordancewith certain embodiments of the invention.

Computational components described and illustrated herein can beimplemented in various forms, for example, as hardware circuits such asbut not limited to custom VLSI circuits or gate arrays or programmablehardware devices such as but not limited to FPGAs, microcontrollers ordigital signal processors (DSPs), or as software program code stored onat least one intangible computer readable medium and executable by atleast one processor, or any suitable combination thereof. A specificfunctional component may be formed by one particular sequence ofsoftware code, or by a plurality of such, which collectively act orbehave or act as described herein with reference to the functionalcomponent in question. For example, the component may be distributedover several code sequences such as but not limited to objects,procedures, functions, routines and programs and may originate fromseveral computer files which typically operate synergistically.

Data can be stored on one or more intangible computer readable mediastored at one or more different locations, different network nodes ordifferent storage devices at a single node or location.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Provided herein, according to certain embodiments of the presentinvention, e.g. as shown and described herein with reference to FIG. 2,is an apparatus for generating a target physical effect, at least oneattribute of which corresponds to at least one characteristic of adigital input signal sampled periodically, the apparatus comprising:

a multiplicity of electrostatic actuator elements, each comprising amoving element moving between first and second electrodes, themultiplicity of electrostatic actuator elements including Nr firstsubsets (R-subsets) of actuator elements and Nc second subsets(C-subsets) of actuator elements, wherein a first partitioning of themultiplicity of actuator elements yields the Nr first subsets(R-subsets) and a second partitioning of the multiplicity of actuatorelements yields the Nc second subsets (C-subsets);

a first plurality of Nr electrical connections (R-wires) interconnectingthe moving elements of actuator elements in each R-subset, such that themoving element of any actuator element in each individual R-subset iselectrically connected to the moving elements of all other actuatorelements in the individual R-subset, and electrically isolated from themoving elements of all actuator elements not in the individual R-subset;

a second plurality of Nc electrical connections (A-wires)interconnecting the first electrodes of actuator elements in eachC-subset, such that the first electrode of any actuator element in eachindividual C-subset is electrically connected to the first electrode ofall other actuator elements in the individual C-subset, and electricallyisolated from all actuator elements not in the individual C-subset;

a third plurality of Nc electrical connections (B-wires) interconnectingthe second electrodes of actuator elements in each C-subset, such thatthe second electrode of any actuator element in each individual C-subsetis electrically connected to the second electrode of all other actuatorelements in the individual C-subset, and electrically isolated from allactuator elements not in the individual C-subset; and

a controller electrically connected to the first, second and thirdpluralities of electrical connections, operative to receive a digitalinput signal, and to apply one of a predetermined, finite set ofelectric potentials to each of the electrical connections respectively,such that resulting movements of the moving elements together producethe desired physical effect.

It is appreciated that R-subsets may have, but need not all have, thesame number of elements. The same is true for the C-subsets. R-subsetsmay or may not intersect with all C-subsets.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 2, the controller is operative to determine,according to the digital input signal, Nr-tuplets of electricalpotential for application to the first plurality of Nr electricalconnections (R-wires) respectively, first Nc-tuplets of electricalpotential for application to the second plurality of Nc electricalconnections (A-wires) respectively, and second Nc-tuplets of electricalpotential for application to the third plurality of Nc electricalconnections (B-wires) respectively.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIGS. 2 and 14, the Nr-tuplets, first Nc-tuplets andsecond Nc-tuplets are determined by the controller such that theirapplication to the first, second and third plurality of electricalconnections respectively causes the moving elements of the multiplicityof actuator elements to produce a physical effect which corresponds toat least one characteristic of the digital input signal.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 1b-1c , each moving element is operative,responsive to potentials applied by the controller, to move from a firstextreme position closer to the first electrode than to the secondelectrode, to a second extreme position closer to the second electrodethan to the first electrode, and back.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 2-3, intersections of any individual one of thefirst subsets of actuator elements and any individual one of the secondsubsets of actuator elements all include a uniform number of actuatorelements (1 or more).

According to certain embodiments, e.g. as shown and described hereinwith reference to FIGS. 4-8 and 10-12, the predetermined, finite set ofelectric potentials includes first and second finite sets of electricalpotential values, the Nr-tuplets of electrical potentials are selectedfrom the first finite sets of electrical potential values; and the firstand second Nc-tuplets of electrical potentials are selected from thesecond finite sets of electrical potential values. At least one memberof the first and second finite sets of electrical potential values maybe zero (ground). Each of the first and second finite set of electricalpotential values may include a member that is zero (ground). At leastone of the first and second finite sets of electrical potential valuesmay have exactly two values. Both of the first and second finite sets ofelectrical potential values may have exactly two values. At least one ofthe first and second finite sets of electrical potential values may haveexactly three values. At least one member of the first finite set ofelectrical potential values may equal at least one member of the secondfinite set of electrical potential values. At least one member of thefirst finite set of electrical potential values may be twice the valueof at least one member of the second finite set of electrical potentialvalues. At least one member of the first finite set of electricalpotential values may be equal in magnitude and opposite in polarity,relative to at least one member of the second finite set of electricalpotential values.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIGS. 2 and 14, the controller is operative toperiodically apply one of the predetermined, finite sets of electricpotentials to each member of the first, second and third pluralities ofelectrical connections respectively. the controller may be operative toperiodically determine, according to the digital input signal,Nr-tuplets of electrical potential for periodic application to the Nrmembers of the first plurality of electrical connections (R-wires)respectively, first Nc-tuplets of electrical potential for periodicapplication to the Nc members of the second plurality of electricalconnections (A-wires) respectively, and second Nc-tuplets of electricalpotential for periodic application to the Nc members of the thirdplurality of electrical connections (B-wires) respectively. applicationof the Nr-tuplets, first Nc-tuplets and second Nc-tuplets of electricalpotential may be synchronous with an actuation clock, such that anNr-tuplet of electrical potential is applied to the first plurality ofNr electrical connections (R-wires), a first Nc-tuplet of electricalpotential is applied to the second plurality of Nc electricalconnections (R-wires), and a second Nc-tuplet of electrical potential isapplied to the third plurality of Nc electrical connections (B-wires),periodically and simultaneously, once every actuation clock cycle, forthe duration of the actuation clock cycle.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 1b-1c , each moving element is operative,responsive to the potential applied by the controller, to move from afirst extreme position, closer to the first electrode than to the secondelectrode, to a second extreme position, closer to the second electrodethan to the first electrode, and back, and where such movements arecompleted within a single actuation clock cycle. Each moving elementmay, e.g. as described herein with reference to FIG. 9, be operative,responsive to the potential applied by the controller, to move from afirst extreme position, closer to the first electrode than to the secondelectrode, to a second extreme position, closer to the second electrodethan to the first electrode, and back, and where such movements arecompleted within k actuation clock cycles, where k is a positiveinteger, e.g. 2 (FIGS. 9, 10 e.g.) or larger.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 2, a manufacturing method is provided, formanufacturing apparatus for generating a physical effect, at least oneattribute of which corresponds to at least one characteristic of adigital input signal sampled periodically, the method comprising:

providing a multiplicity of electrostatic actuator elements, eachcomprising a moving element moving between first and second electrodes,the providing including defining:

-   -   a first partitioning of the multiplicity of actuator elements        into Nr first subsets (R-subsets), and    -   a second partitioning of the multiplicity of actuator elements        into Nc second subsets (C-subsets);

interconnecting the moving elements of actuator elements in eachR-subset, via a first plurality of Nr electrical connections (R-wires),such that the moving element of any actuator element in each individualR-subset is electrically connected to the moving elements of all otheractuator elements in the individual R-subset, and electrically isolatedfrom the moving elements of all actuator elements not in the individualR-subset;

interconnecting the first electrodes of actuator elements in eachC-subset, via a second plurality of Nc electrical connections (A-wires),such that the first electrode of any actuator element in each individualC-subset is electrically connected to the first electrode of all otheractuator elements in the individual C-subset, and electrically isolatedfrom all actuator elements not in the individual C-subset;

interconnecting the second electrodes of actuator elements in eachC-subset, a third plurality of Nc electrical connections (B-wires), suchthat the second electrode of any actuator element in each individualC-subset is electrically connected to the second electrode of all otheractuator elements in the individual C-subset, and electrically isolatedfrom all actuator elements not in the individual C-subset; and

providing a controller electrically connected to the first, second andthird pluralities of electrical connections, operative to receive adigital input signal, and to apply one of a predetermined, finite set ofelectric potentials to each of the electrical connections respectively,such that resulting movements of the moving elements together producethe desired physical effect.

Each moving element may, e.g. as described herein with reference toFIGS. 10, 24, be operative, responsive to the potential applied by thecontroller, to move from a first extreme position, closer to the firstelectrode than to the second electrode, to a second extreme position,closer to the second electrode than to the first electrode, and back,

and wherein, during a single actuation clock cycle, some of themultiplicity of moving elements leave one of their extreme positions anddo not yet reach the other of their extreme positions and others of themultiplicity of moving elements reach one of their extreme positionshaving left the other of their extreme positions during an actuationclock cycle previous to the single actuation clock cycle.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 14, a method is provided for generating aphysical effect, at least one attribute of which corresponds to at leastone characteristic of a digital input signal sampled periodically, themethod comprising:

providing a multiplicity of electrostatic actuator elements, eachcomprising a moving element moving between first and second electrodes,the multiplicity of electrostatic actuator elements including Nr firstsubsets (R-subsets) of actuator elements and Nc second subsets(C-subsets) of actuator elements, wherein a first partitioning of themultiplicity of actuator elements yields the Nr first subsets(R-subsets) and a second partitioning of the multiplicity of actuatorelements yields the Nc second subsets (C-subsets);

providing a first plurality of Nr electrical connections (R-wires)interconnecting the moving elements of actuator elements in eachR-subset, such that the moving element of any actuator element in eachindividual R-subset is electrically connected to the moving elements ofall other actuator elements in the individual R-subset, and electricallyisolated from the moving elements of all actuator elements not in theindividual R-subset;

providing a second plurality of Nc electrical connections (A-wires)interconnecting the first electrodes of actuator elements in eachC-subset, such that the first electrode of any actuator element in eachindividual C-subset is electrically connected to the first electrode ofall other actuator elements in the individual C-subset, and electricallyisolated from all actuator elements not in the individual C-subset;

providing a third plurality of Nc electrical connections (B-wires)interconnecting the second electrodes of actuator elements in eachC-subset, such that the second electrode of any actuator element in eachindividual C-subset is electrically connected to the second electrode ofall other actuator elements in the individual C-subset, and electricallyisolated from all actuator elements not in the individual C-subset; and

using a controller, electrically connected to the first, second andthird pluralities of electrical connections, to receive a digital inputsignal, and to apply one of a predetermined, finite set of electricpotentials to each of the electrical connections respectively, such thatresulting movements of the moving elements together produce the desiredphysical effect.

The physical effect may be sound defining the following attributes:volume; and pitch; wherein the digital input signal has the followingcharacteristics: amplitude; and frequency; and wherein the digital inputsignal's amplitude corresponds to the sound's volume and the digitalinput signal's frequency corresponds to the sound's pitch.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 16, the moving element is operative, responsiveto potentials applied by the controller, to move from a first extremeposition, closer to the first electrode than to the second electrode, toa second extreme position, closer to the second electrode than to thefirst electrode, and back,

and wherein, once per actuation clock cycle, the controller is operativefor computing a net_moves number characterized in that if, during thatindividual clock cycle, m1 moving elements are released from the firstextreme position and m2 moving elements are released from the secondextreme position, and m2−m1=net_moves, the physical effect is producedduring the individual clock cycle.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIGS. 15-23, the controller is additionally operativeto determine, once per clock cycle, application-effective electricalpotentials which, when applied to the first plurality of Nr electricalconnections (R-wires), the second plurality of Nc electrical connections(A-wires), and the third plurality of Nc electrical connections(B-wires) respectively, are operative to effect:

-   -   Release of k1 moving elements from the first extreme position    -   Release of k2 moving elements from the second extreme position        such that k1−k2 is close enough to net_moves to produce a        physical effect which resembles the target physical effect        sufficiently closely for purposes of a given application.

At each actuation clock cycle, the total number of moving elementsreleased from both extreme position may be minimized by releasing zeroelements from at least one of the extreme positions.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 24, at each actuation clock cycle, the totalnumber of moving elements released from both extreme positions isminimized unless a higher total number exists for which k1−k2 is closerto net-moves. Typically, at each actuation clock cycle, If net_moves ispositive or zero: k1=2×net_moves and k2=net_moves. Typically, ifnet_moves is negative: k1=net_moves and k2=2×net_moves.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 15-23, during a single actuation clock cycle,some of the multiplicity of moving elements leave one of their extremepositions and do not yet reach the other of their extreme positions andothers of the multiplicity of moving elements reach one of their extremepositions having left the other of their extreme positions during anactuation clock cycle previous to the single actuation clock cycle andthe application-effective electrical potentials are selected by thecontroller to ensure that any moving elements having been released,previously to the single actuation clock cycle, from one of theirextreme positions reach the opposite extreme position during anappropriate clock cycle.

Each moving element may be operative, responsive to the potentialapplied by the controller, to move from a first extreme position, closerto the first electrode than to the second electrode, to a second extremeposition, closer to the second electrode than to the first electrode,and back, and where such movements are completed within k actuationclock cycles, where k is a positive integer.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIGS. 4-7, 10 and 24:

-   -   Each R-subset includes Nc moving elements    -   Each C-subset includes Nr moving elements    -   R-wires are numbered, arbitrarily, consecutively, or otherwise,        from 0 to Nr−1 thereby to define an ordering thereof. It is        appreciated that numbering as used herein does not include any        physical marking of any element being numbered.    -   A-wires and B-wires are numbered, arbitrarily, consecutively, or        otherwise, from 0 to Nc-1 thereby to define an ordering thereof.    -   Moving elements are numbered such that each moving element has        the number: Nr×C-subset number+R-subset number.

The controller may select the application-effective electric potentialssuch that, at each actuation clock cycle, the numbers of all movingelements currently in the A-position form a continuous wraparoundsequence, and the numbers of all moving elements currently in theB-position also form a continuous wraparound sequence.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 24, the controller selects theapplication-effective electric potentials such that, at each actuationclock cycle, the numbers of all moving elements currently in theA-position form a single continuous wraparound sequence, and the numbersof all moving elements currently in the B-position also form a singlecontinuous wraparound sequence, unless other application-effectiveelectric potentials exist for which k1−k2 is closer to net-moves. at anyactuation clock cycle when the numbers of all moving elements currentlyin the A-position and the numbers of all moving elements currently inthe B-position do not each form a single continuous wraparound sequence,the controller may select the application-effective electric potentialssuch that, at a subsequent actuation clock cycle, the numbers of allmoving elements currently in the A-position again form a singlecontinuous wraparound sequence, and the numbers of all moving elementscurrently in the B-position also again form a single continuouswraparound sequence. At any actuation clock cycle when the numbers ofall moving elements currently in the A-position and the numbers of allmoving elements currently in the B-position do not each form a singlecontinuous wraparound sequence, the controller may select theapplication-effective electric potentials such that, at a subsequentactuation clock cycle, the numbers of all moving elements currently inthe A-position again form a single continuous wraparound sequence, andthe numbers of all moving elements currently in the B-position alsoagain form a single continuous wraparound sequence, unless otherapplication-effective electric potentials exist for which k1−k2 iscloser to net-moves.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 24, the controller may select theapplication-effective electric potentials such that, at each actuationclock cycle, the numbers of all moving elements currently in theA-position form S continuous wraparound sequences, and the numbers ofall moving elements currently in the B-position also form S continuouswraparound sequences, where S is a positive integer. the controller mayselect the application-effective electric potentials such that, at eachactuation clock cycle, the numbers of all moving elements currently inthe A-position form S continuous wraparound sequences, and the numbersof all moving elements currently in the B-position also form Scontinuous wraparound sequences, where S is a positive integer, unlessother application-effective electric potentials exist for which k1-k2 iscloser to net-moves. at any actuation clock cycle when the numbers ofall moving elements currently in the A-position and the numbers of allmoving elements currently in the B-position each form more than Scontinuous wraparound sequences, the controller may select theapplication-effective electric potentials such that, at a subsequentactuation clock cycle, the numbers of all moving elements currently inthe A-position again form only S continuous wraparound sequences, andthe numbers of all moving elements currently in the B-position alsoagain form only S continuous wraparound sequences. at any actuationclock cycle when the numbers of all moving elements currently in theA-position and the numbers of all moving elements currently in theB-position each form more than S continuous wraparound sequences, thecontroller may select the application-effective electric potentials suchthat, at a subsequent actuation clock cycle, the numbers of all movingelements currently in the A-position again form only S continuouswraparound sequences, and the numbers of all moving elements currentlyin the B-position also again form only S continuous wraparoundsequences, unless other application-effective electric potentials existfor which k1−k2 is closer to net-moves.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIGS. 15-23, the controller selects theapplication-effective electric potentials such that the numbers of anymoving elements released from the first extreme position during anyactuation clock cycle immediately follow the numbers of those movingelements most recently released from the first extreme position,wrapping back to 0 after reaching Nr×Nc−1. the controller may select theapplication-effective electric potentials such that the numbers of anymoving elements released from the first extreme position during anyactuation clock cycle immediately follow the numbers of those movingelements most recently released from the first extreme position,wrapping back to 0 after reaching Nr×Nc−1, unless otherapplication-effective electric potentials exist for which k1−k2 iscloser to net-moves. The controller may additionally select theapplication-effective electric potentials such that the numbers of anymoving elements released from the second extreme position during anyactuation clock cycle also immediately follow the numbers of thosemoving elements most recently released from the second extreme position,wrapping back to 0 after reaching Nr×Nc−1. The controller mayadditionally select the application-effective electric potentials suchthat the numbers of any moving elements released from the second extremeposition during any actuation clock cycle also immediately follow thenumbers of those moving elements most recently released from the secondextreme position, wrapping back to 0 after reaching Nr×Nc−1, unlessother application-effective electric potentials exist for which k1−k2 iscloser to net-moves. the controller may select the application-effectiveelectric potentials such that all moving elements released from thefirst extreme position during the same actuation clock cycle are all ina single first C-subset, unless other application-effective electricpotentials exist for which k1−k2 is closer to net-moves. The controllermay additionally select the application-effective electric potentialssuch that all moving elements released from the second extreme positionduring the same actuation clock cycle are all in a single secondC-subset, unless other application-effective electric potentials existfor which k1−k2 is closer to net-moves.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 14, the controller includes, apart from elementselection functionality, some or all of a scaler, a quantizer which mayor may not use dither, at least one level shifter, a low-pass filter anda sample-rate converter.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 13, in the absence of any potentials applied tothe first plurality of Nr electrical connections, the second pluralityof Nc electrical connections, and the third plurality of Nc electricalconnections, such as for example, when the apparatus is powered down,the moving elements may return to a resting position located between thefirst and second extreme positions, and the controller additionallycomprises means to cause one or more of the moving elements to move fromtheir resting position to one of the first and second extreme positions.The controller may be operative for simultaneously causing all of themoving elements within the actuator array to move from their restingposition to one of the first and second extreme positions.

The controller may be operative for causing some of the moving elementsto move from their resting position to the first extreme position, whilesimultaneously causing others of the moving elements to move from theirresting position to the second extreme position.

The controller may effect the movement of moving elements from theirresting position to one of the first and second extreme positions, andmovements of moving elements between their first and second extremepositions, using a single predetermined, finite set of electricpotentials. The differences between the potentials may not be sufficientin magnitude to cause moving elements to move directly from equilibriumat their resting position to one of the extreme positions. Thecontroller may effect the movement of moving elements from their restingposition to one of the first and second extreme positions by applying apredetermined sequence of potentials to one or more members of the firstplurality of Nr electrical connections, the second plurality of Ncelectrical connections, and the third plurality of Nc electricalconnections.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 13, the predetermined sequence may comprise afirst part wherein the controller repeatedly changes one or more of thepotentials applied to the members of the first plurality of Nrelectrical connections, the second plurality of Nc electricalconnections, and the third plurality of Nc electrical connections, suchthat these changes in one or more potentials cause the moving elementsto oscillate around their resting position at their mechanical resonancefrequency; and a second part wherein the controller applies to themembers of the first plurality of Nr electrical connections, the secondplurality of Nc electrical connections, and the third plurality of Ncelectrical connections a set of potentials which maximizes theelectrostatic force attracting each moving elements towards the extremeposition to which it is to be moved. The controller may be operative totime a transition from the first part to the second part to occur at apoint in time where each of the moving elements is closer to the extremeposition to which it is to be moved than to the opposite extremeposition. The changes in one or more potentials during the first partmay occur periodically at a frequency which is twice the mechanicalresonance frequency of the moving elements.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 27, addressing noise results from nonzerodifferences (addressing errors) between k1−k2 and net_moves during oneor more actuation clock cycles, the addressing noise having a frequencyspectrum, wherein the controller includes an addressing noise shapingloop operative to shape the frequency spectrum of the addressing noise,such that addressing noise energy is reduced within a frequency band ofinterest and increased outside the band of interest. The noise shapingloop may have a loop filter having an impulse response and receiving theaddressing noise, such that the frequency spectrum of the addressingnoise is shaped according to an addressing noise transfer functiondetermined by the impulse response.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 29, quantization noise results from the number ofactuator elements in the actuator array being less than the number ofpossible values that the digital input signal can assume, thequantization noise having a frequency spectrum, and the controllerincludes a quantization noise shaping loop operative to shape thefrequency spectrum of the quantization noise, such that quantizationnoise energy is reduced within a frequency band of interest andincreased outside the band of interest. The noise shaping loop may havea loop filter having an impulse response and receiving quantizationnoise, such that the frequency spectrum of the quantization noise isshaped according to a quantization noise transfer function determined bythe impulse response.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 28, the controller includes a noise shaping loopoperative to shape the frequency spectra of both of the addressing noiseand the quantization noise, such that both addressing noise energy andquantization noise energy are reduced within a frequency band ofinterest and increased outside the band of interest. The noise shapingloop may have a single loop filter having a single impulse response andreceiving the sum of the addressing noise and the quantization noise,such that the frequency spectra of both of the addressing noise and thequantization noise are shaped according to a single noise transferfunction determined by the single impulse response.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 29, addressing noise results from nonzerodifferences (addressing errors) between k1−k2 and net_moves during oneor more actuation clock cycles, the addressing noise having anaddressing noise spectrum, and the apparatus also suffers fromquantization noise resulting from the number of actuator elements in theactuator array being less than the number of possible values that thedigital input signal can assume, the quantization noise having aquantization noise spectrum, and the controller includes an addressingnoise shaping loop operative to shape the frequency spectrum of theaddressing noise and a quantization noise shaping loop operative toshape the frequency spectrum of the quantization noise, such that bothaddressing noise energy and quantization noise energy are reduced withinrespective frequency bands of interest and increased outside the bandsof interest. The addressing noise shaping loop may have a first loopfilter having a first impulse response and receiving the addressingnoise, and the quantization noise shaping loop may have a second loopfilter having a second impulse response and receiving the quantizationnoise, such that the frequency spectrum of the addressing noise isshaped according to a first noise transfer function determined by thefirst impulse response, and the frequency spectrum of the quantizationnoise is shaped according to a second noise transfer function determinedby the second impulse response.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 13, the duration of the second part is at leasthalf the mechanical resonance period (Tres) of the moving elements. Theset of potentials may be selected from among the predetermined, finiteset of electric potentials, and does not change during the second part.

According to certain embodiments, e.g. as shown and described hereinwith reference to FIG. 24, the controller generates, at each actuationclock cycle,

Nr R-signals r0 to r(Nr−1) controlling the potential applied to each ofthe R-wires R0 to R(Nr−1),

Nc A-signals a0 to a(Nc−1) controlling the potential applied to each ofthe A-wires A0 to A(Nc−1), and

Nc B-signals b0 to b(Nc−1) controlling the potential applied to each ofthe B-wires B0 to B(Nc−1).

The assignment of R-signals to R-wires, A-signals to A-wires andB-signals to B-wires may be fixed, e.g. such that

each of the R-signals r0 to r(Nr−1) always controls the same R-wire,

each of the A-signals a0 to a(Nc−1) always controls the same A-wire,

and each of the B-signals b0 to b(Nc−1) always controls the same B-wire.

Optionally, the controller changes the assignment of R-signals toR-wires and/or the assignment of A-signals to A-wires and B-signals toB-wires during operation of the apparatus.

The changes in the assignment of R-signals to R-wires and/or theassignment of A-signals to A-wires and B-signals to B-wires may occurperiodically.

The changes in the assignment of R-signals to R-wires and/or theassignment of A-signals to A-wires and B-signals to B-wires may occursynchronously with the actuation clock.

The changes in the assignment of R-signals to R-wires and/or theassignment of A-signals to A-wires and B-signals to B-wires may alterthe order in which moving elements are subsequently released from one ofthe extreme positions.

The changes in the assignment of R-signals to R-wires and/or theassignment of A-signals to A-wires and B-signals to B-wires may shapethe frequency spectrum of mismatch noise resulting from differences inthe magnitude of the physical effect produced by each actuator element,such that the physical effect produced by the apparatus as a whole moreclosely resembles the target physical effect. The shaping of thefrequency spectrum of the mismatch noise may for example comprisereducing the magnitude of peaks in the frequency spectrum of themismatch noise.

Typically, the changes in the assignment of R-signals to R-wires and/orthe assignment of A-signals to A-wires and B-signals to B-wires do notresult in any immediate change in any of the potentials applied to theR-wires, A-wires and B-wires.

Typically, the changes in the assignment of R-signals to R-wires and/orthe assignment of A-signals to A-wires and B-signals to B-wires do notresult in any immediate change in the position of any moving elementwithin the actuator array.

The term “immediate” refers to an occurrence at substantially the sametime that the changes in the assignment of R-signals to R-wires and/orthe assignment of A-signals to A-wires and B-signals to B-wires “occur.

The changes in the assignment of R-signals to R-wires may includeswapping of two R-signals, such that a first R-wire previouslycontrolled by a first R-signal becomes controlled by a second R-signal,and a second R-wire previously controlled by the second R-signal becomescontrolled by the first R-signal.

The controller may be operative to identify sets of swappable R-signals,and where at least one of the sets of swappable R-signals has more thanone member, to determine a new assignment of R-signals to R-wires.

The controller may be operative to identify sets of swappable R-signalssuch that, for any particular R-signal within a set of swappableR-signals, the moving elements in the R-subset whose R-wire is currentlycontrolled by the particular R-signal, and the moving elements in allR-subsets whose R-wire is currently controlled by another R-signalwithin the same set of swappable R-signal, are all in the same positionand (if in movement) moving in the same direction.

The controller may be operative to identify sets of swappable R-signalssuch that, for any particular R-signal within a set of swappableR-signals, and for any number i from 0 up to and including Nc−1, themoving element at the intersection of C-subset i and the R-subset whoseR-wire is currently controlled by the particular R-signal is in the sameposition and (if in movement) moving in the same direction as the movingelement at the intersection of C-subset i and any other R-subset whoseR-wire is currently controlled by any other of the R-signals within thesame set of swappable R-signals.

The controller may employ a pseudo-random number generator fordetermining the new assignment of R-signals to R-wires.

The changes in the assignment of A-signals to A-wires and B-signals toB-wires may include swapping of two A-signals and the respectiveB-signals, e.g. such that a first A-wire and a first B-wire, previouslycontrolled by a first A-signal and a first B-signal respectively, becomecontrolled by a second A-signal and a second B-signal respectively, anda second A-wire and a second B-wire, previously controlled by the secondA-signal and the second B-signal respectively, become controlled by thefirst A-signal and the first B-signal respectively.

The controller may be operative to identify sets of swappable A-signalsand respective B-signals, and where at least one of the sets ofswappable A-signals and respective B-signals has more than one member,to determine a new assignment of A-signals to A-wires and respectiveB-signals to B-wires.

The controller may be operative to identify sets of swappable A-signalsand respective B-signals, such that, for any particular A-signal andparticular B-signal within a set of swappable A-signals and respectiveB-signals, the moving elements in the C-subset whose A-wire and B-wireare currently controlled by the particular A-signal and particularB-signal respectively, and the moving elements in all C-subsets whoseA-wire and B-wire are currently controlled another A-signal and itsrespective B-wire within the same set of swappable A-signals andrespective B-signals, are all in the same position and (if in movement)moving in the same direction.

The controller may be operative to identify sets of swappable A-signalsand respective B-signals, such that, for any particular A-signal andparticular B-signal within a set of swappable A-signals and respectiveB-signals, and for any number i from 0 up to and including Nr−1, themoving element at the intersection of R-subset i and the C-subset whoseA-wire and B-wire are currently controlled by the particular A-signaland the particular B-signal respectively is in the same position and (ifin movement) moving in the same direction as the moving element at theintersection of R-subset i and any other C-subset whose A-wire andB-wire are currently controlled by one of the A-signals and itsrespective B-signal within the same set of swappable A-signals andrespective B-signals.

The controller may employ a pseudo-random number generator fordetermining the new assignment of A-signals to A-wires and respectiveB-signals to B-wires.

The controller may be operative to identify sets of swappable R-signalssuch that, for each particular R-signal within a set of swappableR-signals, the electrical potential currently applied to the R-wirecontrolled by said particular R-signal is the same as the electricalpotential currently applied to any R-wire controlled by any otherR-signal within the same set of swappable R-signals.

The controller may be operative to identify sets of swappable A-signalsand respective B-signals such that, for each particular A-signal andrespective B-signal within a set of swappable A-signals and respectiveB-signals, the electrical potentials currently applied to the A-wire andrespective B-wire controlled by said particular A-signal and respectiveB-signal are the same as the electrical potentials currently applied toany A-wire and respective B-wire controlled by any other A-signal andrespective B-signal within the same set of swappable A-signals andrespective B-signals.

The term “currently” is intended to include an occurrence:

-   -   At the time the controller does the “identifying” of swappable        sets; or    -   During the actuation clock cycle in which the controller does        the “identifying” of swappable sets; or    -   During the current actuation clock cycle.

Reference is now made to FIGS. 1A to 1C which are cross-sectionalillustrations of one type of double-sided electrostatic actuator elementto which the present invention can be applied. The actuator elementincludes a moving element 120 mechanically connected to the stationaryportions of the actuator element by means of a suitable bearing 150 suchas a flexure or spring. The bearing 150 defines an axis 125 along whichthe moving element 120 can travel, prevents the moving element 120 fromtravelling in other directions, and defines an at-rest position of themoving element 120. The actuator element further comprises twoelectrodes 130 and 140, also referred to hereinafter as “A-electrode”and “B-electrode” respectively, disposed on opposite sides of the movingelement 120. The moving element 120 is separated from the electrodes 130and 140 by spacers 180 and 190. Dimples 210 and 220 are formed on thesurfaces of the electrodes 130 and 140 respectively which each face themoving element 120.

FIG. 1A shows the moving element 120 in its resting position, with novoltage applied between the moving element 120 and either electrode 130and 140.

Applying a voltage between the moving element and either electrodeproduces an electrostatic force attracting the moving element towardsthat electrode, the magnitude of the electrostatic force beingproportional to the magnitude of the voltage applied, and inverselyproportional to the square of the separation distance between facingsurfaces of moving element 120 and the respective electrode. At the sametime, any movement of the moving element 120 away from its restingposition causes bearing 150 to exert on the moving element 120 a springforce pulling it back towards its resting position. Moving element 120may also be affected by other forces such as damping or friction forceswhich may either occur naturally or be deliberately introduced forpractical reasons such as to improve long-term reliability. However,such additional forces are not required for the purposes of the presentinvention. The moving element 120 may reach an equilibrium positionwhere the sum of all forces acting on it is zero, or it may be latchedas described under FIGS. 1B and 1C.

FIG. 1B shows moving element 120 latched in a first extreme position, asclose as possible to A-electrode 130 and as far as possible fromB-electrode 140, also referred to hereinafter as the “A-position”.Typically, moving element 120 reaches this position as a result of avoltage V_(A) being applied between A-electrode 130 and moving element120, generating an electrostatic force, also referred to hereinafter as“A-force”, attracting moving element 120 towards A-electrode 130. Asmoving element 120 approaches A-electrode 130, the A-force increasesinversely proportional to the square of the separation distance betweenfacing surfaces of moving element 120 and electrode 130, whereas thespring force pulling moving element 120 back towards its restingposition increases proportionally to its deflection from its restingposition. Depending on the spring constant of bearing 150 and on therange of V_(A), a critical point may exist along axis 125 where A-forceand the spring force are equal and any further travel of moving element120 towards A-electrode 130 causes the A-force to grow more quickly thanthe spring force. If moving element 120 moves even marginally beyondthis critical point, and assuming that V_(A) remains constant, thebalance of forces causes moving element 120 to accelerate towardsA-electrode 130 until it makes contact with dimples 210, a processreferred to hereinafter as “latching”. After latching, the magnitude ofV_(A) sufficient to hold moving element 120 in this position (referredto hereinafter as “hold voltage”), is smaller than the magnitude ofV_(A) sufficient to achieve latching of moving element 120 into theA-position (referred to hereinafter as “latching voltage”).

When moving element 120 is latched in the A-position and a secondvoltage V_(B) is applied between B-electrode 140 and moving element 120,the electrostatic force resulting from V_(B) is significantly smaller inmagnitude than the A-force resulting from a V_(A) of equal magnitude.Hence, the presence of a non-zero V_(B) only marginally increases themagnitude of the hold voltage sufficient to keep moving element 120latched in the A-position.

If V_(A) subsequently falls below the hold voltage, the A-force becomessmaller in magnitude than the spring force, causing moving element 120to move away from the A-position and towards its resting position, aprocess referred to hereinafter as “release”. With both V_(A) and V_(B)equal to zero, moving element 120 then oscillates around its restingposition with its frequency of oscillation, also referred to hereinafteras its “mechanical resonance frequency”, determined primarily by themass of moving element 120 and the spring constant of bearing 150(neglecting damping), and the amplitude of oscillation graduallydecreasing as a result of friction, air damping or other energy loss.Alternatively, in the presence of a non-zero V_(B) of sufficientmagnitude, moving element 120 is latched into a second extreme position,as close as possible to B-electrode 140 and as far as possible fromA-electrode 130, also referred to hereinafter as the “B-position”.

According to one embodiment of the present invention, the controller mayadjust V_(A) and V_(B) such that moving element 120 is always either inthe A-position or the B-position, or transitioning between these twopositions; i.e. during normal operation, moving element 120 neversettles in its resting position or any other position except the twoextreme positions.

When moving element 120 reaches its resting position during transitionsbetween the two extreme positions, it has non-zero kinetic energy andlinear velocity relative to electrodes 130 and 140 and thereforecontinues to travel towards its new extreme position until its kineticenergy is absorbed by bearing 150. Since latching moving element 120from a position closer to its new extreme position requires a lowerelectrostatic force than latching moving element 120 into that sameextreme position from equilibrium at its resting position, latchingvoltages are lower for transitions between extreme positions than forlatching from rest.

The purpose of dimples 210 is to maintain an air gap 240, therebyallowing air to flow through holes 270 in the electrode 130 and into thespace between the moving element 120 and first electrode 130 more easilythan would be the case without an air gap, thereby facilitating a fasterrelease of moving element 120 from the A-position. If dimples 210include electrically insulating material, they may also serve toinsulate moving element 120 from electrode 130. If dimples 210 includeelectrically conductive material, then some other means of electricalinsulation may be employed, such as coating at least one of movingelement 120 and electrode 130 with electrically insulating material.

FIG. 1C shows the moving element 120 latched in the B-position, as closeas possible to electrode 140 and as far as possible from electrode 130.Latching of the moving element 120 into the B-position and release fromthe B-position may be achieved in a manner analogous to that describedunder FIG. 1B above, reversing the roles of A-electrode 130 andB-electrode 140, that of V_(A) and V_(B), and that of A-force andB-force. The function of dimples 220 and air gap 250 is analogous tothat of dimples 210 and air gap 240 described above. In certainembodiments, the actuator element's geometry is substantially symmetricabout the plane of moving element 120, resulting in hold and latchingvoltages for the B-position substantially equal to those for theA-position. Alternatively, the actuator element's geometry may beasymmetric; for example, spacers 180 and 190 may differ in thickness,resulting in two different latching voltages for the A-position andB-position respectively; and/or dimples 210 and 220 may differ inheight, resulting in two different hold voltages.

Suitable materials and manufacturing techniques for the production ofactuator elements as shown in FIG. 1A-C and closely related types ofactuator elements are discussed in co-owned WO2011/111042(“Electrostatic Parallel Plate Actuators Whose Moving Elements AreDriven Only By Electrostatic Force and Methods Useful in ConjunctionTherewith”), published 15 Sep. 2011.

The present invention does not depend on any particular materials ormanufacturing techniques.

It is appreciated that the polarity of voltages V_(A) and V_(B) can bereversed without affecting operation of the actuator element, since bothelectrostatic forces are the same, regardless of the polarity of thesevoltages.

The orientation of the devices shown and described herein relative tothe horizontal need not be as shown. For example, the apparatus of FIGS.1A-1C may be disposed such that the layers are horizontal, as shown, ormay for example be disposed such that the layers are vertical. Also, theapparatus may be set on its side or may be inverted, if desired, suchthat the electrode layer 140 is atop the moving element 120 rather thanvice versa. According to certain embodiments, the force of gravity isnegligible, since the forces exerted on the moving element by thebearing 150 and the electrostatic forces generated by the electrode orelectrodes are many orders of magnitude larger than gravitationalforces.

The term “air gap” is used herein merely by way of example since theapparatus of the present invention normally operates in air however thisneed not be the case and alternatively, for example, the apparatus mayoperate in any other suitable medium.

It is also appreciated that the dimples shown in FIGS. 1A to 1C are notrequired for the purposes of the present invention. Furthermore, dimplescan be formed on the surface of the moving element 120 instead of theelectrodes 210 and 220, or mechanical limiters, e.g. as described inFIG. 2 in co-owned WO2011/111042 (“Electrostatic Parallel PlateActuators Whose Moving Elements Are Driven Only By Electrostatic Forceand Methods Useful in Conjunction Therewith”), published 15 Sep. 2011,may be used instead of dimples.

FIG. 2 is a simplified schematic diagram of an actuator array inaccordance with certain embodiments of the invention, comprising aplurality of electrostatic actuator elements 110, which may, forexample, be of the type shown and described herein e.g. with referenceto FIGS. 1A-1C.

The actuator elements 110 are partitioned into Nr first subsets,referred to hereinafter as “R-subsets”, whose moving elements areelectrically interconnected, resulting in a set of Nr interconnections400, referred to hereinafter as “R-wires”. Additionally, the actuatorelements 110 are also partitioned into Nc second subsets, referred tohereinafter as “C-subsets”, whose A-electrodes and B-electrodesrespectively are electrically interconnected, resulting in a first setof Nc interconnections 410, referred to hereinafter as “A-wires”, forthe A-electrodes and a second set of Nc interconnections 420, referredto hereinafter as “B-wires”, for the A-electrodes.

In the Figure, Nr=Nc=3, however the subsets may contain any number ofactuator elements. In certain embodiments, all R-subsets contain Ncactuator elements, all C-subsets contain Nr actuator elements, and thetotal number of moving elements in the array is Nr×Nc. In FIG. 2, theR-subsets are arranged in rows and the C-subsets in columns, however anyother layout of actuator elements may also be used.

Each R-wire, A-wire and B-wire is also connected to a controller 50.Thus, the total number of electrical interconnections between the arrayand the controller 50 is Nr+2Nc, whereas implementations with dedicatedinterconnections for each actuator element may employ more suchinterconnections. For example, providing separate interconnections foreach moving element, each A-electrode and each B-electrode may employ3×Nr×Nc interconnections; alternatively, providing separateinterconnections for each moving element plus one shared connection eachfor all A-electrodes and all B-electrodes may employ (Nr×Nc)+2interconnections, e.g. as described in co-owned WO2011/111042(“Electrostatic Parallel Plate Actuators Whose Moving Elements AreDriven Only By Electrostatic Force and Methods Useful in ConjunctionTherewith”), published 15 Sep. 2011.

Actuator arrays of the type described may be manufactured, for example,on a single monolithic die of silicon or other semiconductors or certainmetals, using MEMS fabrication techniques e.g. as described in co-ownedWO2011/111042 (“Electrostatic Parallel Plate Actuators Whose MovingElements Are Driven Only By Electrostatic Force and Methods Useful inConjunction Therewith”), published 15 Sep. 2011.

FIG. 3 is a simplified schematic diagram of an actuator array inaccordance with certain embodiments of the invention, similar to thearray shown in FIG. 2, but where the R-subsets do not coincide with rowsand the C-subsets do not coincide with columns. The array comprises 64actuator elements 110, partitioned into eight R-subsets and fourC-subsets. Each R-subset has one R-wire, labeled R0 to R7 respectively,and each C-subset has one A-wire and one B-wire, labeled A0 to A3 and B0to B3 respectively. Every intersection of one R-subset and one C-subsetcontains two actuator elements. Every R-subset contains four actuatorelements from one row and four actuator elements from another row; forexample, R-subset 1, associated with R-wire R1, contains the left-handhalf of the top row and the right-hand half of the second row from thetop. Every C-subset contains all the actuator elements of two adjacentcolumns; for example, C-subset 1, associated with A-wire A1 and B-wireB1, contains the third and fourth columns from the left.

Actuator arrays constructed in accordance with the invention may havetheir actuator elements laid out in any pattern, and may have any numberof actuator elements at each intersection of one R-subset and oneC-subset. Certain embodiments have the same number of actuator elementsat each such intersection.

The terms “latching voltage” and “hold voltage” for a single, specificactuator element have been defined previously with reference to FIG. 1B.In the following, these terms are defined for an actuator array, whoseactuator elements may not all be exactly identical. Additionally, theterm “release voltage” is also defined below for use hereinafter.

-   -   “Latching voltage” V_(L) means a voltage of only just sufficient        magnitude to reliably latch any of the moving elements within        the array into either its A-position or its B-position as        described with reference to FIG. 1B, after the moving element        has been released from the opposite extreme position. This        latching voltage for an actuator array is typically slightly        higher than the latching voltage for an individual actuator        element previously defined with reference to FIG. 1B, e.g.        because: (1) since the geometry of individual actuator elements        may vary due to manufacturing tolerances, each individual        actuator element may have a slightly different latching voltage;        the V_(L) defined here typically exceed all of them by        definition. (2) likewise, asymmetry in an actuator element's        geometry may produce two different latching voltages for its        A-position and B-position, respectively; in this case, the V_(L)        defined here typically exceeds the higher of the two. (3)        depending on the actuator array's intended usage, actuator        elements 110 may be subject to environmental conditions such as        mechanical shock (e.g. in portable/handheld applications),        magnetic fields, or air flow, which may produce additional        forces on their moving elements 120. In order for latching to be        reliable, the V_(L) defined here are typically sufficient to        overcome such additional forces under the environmental        conditions for which the array is designed.    -   “Hold voltage” V_(H) means a voltage of only just sufficient        magnitude to hold any of the moving elements within the array in        either of the two extreme positions. This hold voltage will        typically be slightly higher than the hold voltage for an        individual actuator element defined with reference to FIG. 1B,        for the same reasons described above with reference to “latching        voltage”.    -   “Release voltage” V_(R) means a voltage whose magnitude is only        just sufficiently low to release any of the actuator elements        within the array from either of its two extreme positions. For        an ideal actuator element, the difference between V_(R) and        V_(H) is infinitesimal; however, in a real array, there is a        finite difference between V_(R) and V_(H) due to the        manufacturing tolerances, asymmetry and environmental conditions        described above with reference to “latching voltage”.

The present invention, according to certain embodiments, employs anactuator array's hold voltage V_(H) sufficiently low in magnitude to notinduce any individual actuator element to latch into either extremeposition.

FIG. 4 is a simplified representation of an actuator array in accordancewith certain embodiments of the invention, comprising sixteen actuatorelements partitioned into four R-subsets and four C-subsets, analogouslyto the actuator array shown in FIG. 2. R-wires are labeled R0 to R3,A-wires A0 to A3 and B-wires B0 to B3. Each square represents oneactuator element 110. The actuator element located at the intersectionof R-subset 1 and C-subset 2, also referred to hereinafter as the“selected element” and labeled 111, is currently latched in theA-position and is to be moved into the B-position. Hence, the task ofcontroller 50 in this example is to apply suitable electric potentialsto the array's R-wires, A-wires and B-wires such that the selectedelement is released from the A-position and latched into the B-position,while keeping all other actuator elements within the array, alsoreferred to hereinafter as “unselected elements”, latched in whicheverof the two extreme positions they currently are. Within each square inFIG. 4, the top line refers to the magnitude of V_(A) and the bottomline to the magnitude of V_(B) sufficient to achieve this. For theselected element, the magnitude of V_(A) is equal to or less than therelease voltage V_(R) and the magnitude of V_(B) equal to or larger thanthe latching voltage V_(L); whereas for all unselected elements, themagnitude of both V_(A) and V_(B) is equal to or higher than the holdvoltage V_(H).

This can be achieved by:

-   -   applying a first voltage V_(RS) (“selected R-voltage”) to the        R-wire connected to the selected element, also referred to        hereinafter as the “selected R-wire”, in this case R1, while        applying a second voltage V_(RU) (“unselected R-voltage”) to all        other R-wires; this process is referred to hereinafter as        “selecting” an R-wire, or the R-subset associated with an        R-wire; and    -   applying a third voltage V_(CR) (“releasing C-voltage”) to the        A-wire or B-wire connected to the electrode from which the        selected element is to be released, also referred to hereinafter        as the “releasing wire”, in this case A2, while applying a        fourth voltage V_(CL) (“latching C-voltage”) to the A-wire or        B-wire connected to the electrode to which the selected element        is to be latched, also referred to hereinafter as the “latching        wire”, in this case B2, and also applying a fifth voltage V_(CU)        (“unselected C-voltage”) to all other A-wires and all other        B-wires, also referred to hereinafter collectively as        “unselected” A-wires and B-wires; this process is referred to        hereinafter as “selecting” a C-subset, and the C-subset        containing the releasing wire and the latching wire is referred        to hereinafter as the “selected C-subset”.

“Drive schemes” described below with reference to FIGS. 5 to 8, areoperative for applying appropriate voltages to the R-wires, A-wires andB-wires, such that the following six conditions below are satisfied:|V _(RS) −V _(CR) |≦V _(R)  1.

-   -   Satisfying this condition ensures successful release of the        selected element from its current latched position. In certain        embodiments it may be desirable to maximize the moving element's        acceleration away from the electrode to which it is currently        latched, also referred to hereinafter as the “releasing        electrode”; in this case it may be preferable to have        |V_(RS)−V_(CR)|=0V as this completely eliminates the        electrostatic force attracting the moving element to the        releasing electrode, as opposed to only reducing this        electrostatic force.        |V _(RS) −V _(CL) |≧V _(L)  2.    -   Satisfying this condition ensures successful latching of the        selected element into its new extreme position.        |V _(RS) −V _(CU) |≧V _(H)  3.    -   Satisfying this condition prevents release of any unselected        actuator elements located in the selected R-subset.        |V _(RU) −V _(CR) |≧V _(H)  4.    -   Satisfying this condition prevents release of any unselected        actuator elements located in the selected C-subset and currently        latched in the same position as the selected element.        |V _(RU) −V _(CL) |≧V _(H)  5.    -   Satisfying this condition prevents release of any unselected        actuator elements located in the selected C-subset and latched        in the extreme position opposite the selected element's current        position.        |V _(RU) −V _(CU) |≧V _(H)  6.    -   Satisfying this condition prevents release of unselected        actuator elements located at the intersections of any unselected        R-subset and any unselected C-subset, and latched in either of        the two extreme positions.

The method described herein may also be used to move actuator elementsfrom the B-position to the A-position; in that case, the releasing wireis a B-wire and the latching wire is an A-wire. For example, if theselected element 111 is in the B-position, it may be moved into theA-position by applying V_(RS) to R1, V_(CL) to A2 and V_(CR) to B2.Since selecting more than one R-subset and/or more than one C-subset atthe same time selects all actuator elements located at the intersectionof any selected R-subset and any selected C-subset, the same method mayalso be used to move more than one moving element from one extremeposition to the other. For example, applying V_(RS) to R2 and R3, V_(cL)to B0 and B1, and V_(CR) to A0 and A1 moves all moving elements in thebottom left quadrant in FIG. 4 from the A-position to the B-position,assuming they are in the A-position to begin with. Any selected actuatorelements whose moving element is already in the B-position would remainlatched in the B-position.

In certain embodiments, the time during which a moving element movesfrom one extreme position to the other (including its release from thefirst extreme position and latching into the second extreme position) isapproximately half of the resonance period T_(res) of the selectedelement, where T_(res) is the inverse of its mechanical resonancefrequency described previously with reference to FIG. 1B. The timededicated to such a movement may be somewhat longer than T_(res)/2, e.g.if there is significant friction or damping, or it may be somewhatfaster than T_(res)/2, e.g. if the magnitude of V_(RS)−V_(CL) issufficiently high to significantly accelerate the movement. However, incertain embodiments, it is close to T_(res)/2.

In order to ensure successful latching of moving elements, theapplication of V_(RS) to the selected R-wire, V_(CR) to the releasingwire, and V_(CL) to the latching wire, is timed to last long enough forthe slowest moving element within the array (allowing for variations dueto manufacturing tolerances) to complete a movement, i.e. typicallyslightly longer than T_(res)/2. After this time has elapsed, theselected element is latched in its new position, and the selectedR-wire, A-wire and B-wire typically become unselected, i.e. thecontroller applies V_(RU) to the formerly selected R-wire and V_(CU) tothe former latching wire and releasing wire. The controller may thenmove other moving elements between their extreme positions by selectingother R-subsets and/or C-subsets. In certain embodiments, the voltagesapplied to R-wires, A-wires and B-wires are all sampled in accordancewith a clock, referred to hereinafter as the “actuation clock”, whosefrequency is typically slightly below double the moving elements'mechanical resonance frequency.

FIG. 5 illustrates the actuator array of FIG. 4 operating according towhat is referred to hereinafter as “drive scheme 1”. Drive scheme 1 ischaracterized in that:V _(RS) =V _(CR) ≧V _(H)V _(RU)=0V _(CL) ≧V _(L) +V _(RS)V _(CU)≧2×V _(RS)

Within each square in FIG. 5, the top line refers to the magnitude ofV_(A) and the bottom line to the magnitude of V_(B). It can be seen thatthis drive scheme fulfills the six conditions described above withreference to FIG. 4, and also has a number of additional usefulproperties, e.g.:

-   -   Any number of R-subsets and any number of C-subsets may be        selected; all actuator elements located at the intersection of        any selected R-subset and any selected C-subset are selected,        all other actuator elements are unselected.    -   Any moving element which is already latched in the desired new        position (e.g. in this example, in the B-position), remains in        that position. Hence, drive scheme 1 can be used to control a        subset of actuator elements which may not all have their moving        elements latched in the same position, or whose current latched        position may be unknown.    -   It fulfills the stricter version of the first of the six        conditions above (|V_(RS)−V_(CR)|=0V), thereby minimizing the        time during which selected elements are released from their        current latched position.

In order to permit selection of any desired R-subset or R-subsets, acontroller implementing drive scheme 1 is operative for applying eitherof two voltages (V_(RS) or V_(RU)) to each R-wire 400. Likewise, inorder to permit selection of any desired C-subset or C-subsets, andsince each A-wire and each B-wire can be either a releasing wire, alatching wire or an unselected wire at a given time, such a controlleris operative for applying either of three voltages (V_(CR), V_(CL) orV_(CU)) to each A-wire 410 and to each B-wire 420.

FIG. 6 illustrates the actuator array of FIGS. 4 and 5 operatingaccording to what is referred to hereinafter as “drive scheme 2”. Thisdrive scheme is characterized by:V _(RS) =V _(CR) ≧V _(H)V _(RU)=0V _(CL) =V _(CU) ≧V _(L) +V _(RS)

The difference between the two drive schemes is that the minimummagnitude of V_(CU) has been increased from 2×V_(H) to V_(L)+V_(H).Since, by definition, V_(L) is larger than V_(H) (as described abovewith reference to FIG. 4), drive scheme 2 satisfies the six conditions.A controller implementing drive scheme 2 has the advantage that it iscapable of applying either of only two voltages (V_(CR) orV_(CL)/V_(CU)) to each A-wire 410 and to each B-wire 420, resulting inreduced complexity and cost compared to drive scheme 1 where each A-wireand B-wire can take three different voltages.

Under drive scheme 2, V_(A) and V_(B) of those unselected actuatorelements in unselected C-subsets are higher in magnitude than with drivescheme 1 and higher than required to keep the unselected elementslatched in their current extreme position, but no higher than thehighest V_(A) and V_(B) already occurring under drive scheme 1 (whichequals the difference between V_(CL) and V_(RU) and occurs in actuatorelements located at the intersections of unselected R-subsets andselected C-subsets). This is generally not a drawback.

FIG. 7 illustrates the actuator array of FIGS. 4 to 6 operatingaccording to what is referred to hereinafter as “drive scheme 3”. Drivescheme 3 is characterized by:V _(RS) =V _(CR)=0V _(RU) =≦−V _(H)V _(CL) =V _(CU) ≧V _(L)

This produces the same V_(A) and V_(B) as drive scheme 2 in all actuatorelements. However, compared to drive scheme 2, V_(H) has been subtractedfrom the voltages applied to all R-wires, A-wires and B-wires.

It is appreciated that adding or subtracting any other given voltagefrom all R-wire, A-wire and B-wire voltages also results in driveschemes equivalent to drive scheme 2. Furthermore, the polarity of drivevoltages in any drive scheme may be inverted without affecting theoperation of the actuator array as long as V_(A) and V_(B) retain thesame magnitude as under drive scheme 2. For example, the following drivescheme, referred to hereinafter as “drive scheme 4”, is equivalent todrive schemes 2 and 3:V _(RS) =V _(CR) ≦−V _(H)V _(RU)=0V _(CL) =V _(CU)≦−(V _(L) +V _(RS))Likewise, the following drive scheme, referred to hereinafter as “drivescheme 5”, is equivalent to drive schemes 2 to 4:V _(RS) =V _(CR)=0V _(RU) =≧V _(H)V _(CL) =V _(CU) ≦−V _(L)

FIG. 8 is a summary of drive schemes 1 to 5 in tabular form.

FIG. 9 is a graph of electrostatic and spring forces acting on a movingelement 120, constructed as described with reference to FIGS. 1A to 1C,as a function of its deflection along axis 125 and towards theA-electrode 130. In the example of FIG. 9, the thickness of spacers 180and 190 is 3 μm. The horizontal axis represents the deflection of themoving element from its resting position towards the A-electrode, withnegative values indicating a deflection away from the A-electrode andtowards the B-electrode. The A-force, B-force, spring force (previouslydefined with reference to FIGS. 1B, 1C and 1A respectively) and totalforce are plotted on the vertical axis.

In the example of FIG. 9, V_(B) and hence also the B-force are zero,whereas V_(A) is nonzero and produces a nonzero A-force. Thus the totalforce exerted on moving element 120 is the sum of the A-force and springforce. It can be seen that there are two equilibrium points where thetotal force acting on moving element 120 is zero. The first equilibriumpoint is close to the resting position, i.e. slightly to the right ofthe origin in the graph of FIG. 9, and is a stable equilibrium, i.e. ifthe moving element 120 is a small distance away to either side of theequilibrium point then the balance of forces acting on it will cause itto move towards the first equilibrium point. The second equilibriumpoint occurs closer to the A-electrode, at a deflection of approximately2 μm, and is an unstable equilibrium. If the moving element 120 is asmall distance further away from A-electrode 130 than this secondequilibrium point then the balance of forces acting on it will cause itto move towards the first equilibrium point. If moving element 120 is asmall distance closer to the A-electrode 130 than the second equilibriumpoint then the balance of forces acting on it will cause it to movetowards the A-electrode and be latched in the A-position.

The drive schemes described below are suitable for embodiments in whichthe motion of a selected element between its two extreme positions in anactuator element may be dominated by different effects at differentpoints in time.

Immediately after the selected element is released from its currentlatched position, the spring force exerted on its moving element bybearing 150 dominates its motion, propelling it towards its newlocation. The electrostatic force pulling moving element 120 backtowards its previous latched position is zero under any of the driveschemes described above. Although the drive schemes previously discussedprovide an electrostatic force attracting moving element 120 towards thelatching electrode, this electrostatic force is not actually required atthis time, since the desired motion can be achieved by the spring forcealone. In any case, the electrostatic force, if present, is relativelyweak at this time, because moving element 120 is relatively far from thelatching electrode. Hence, the voltage between the latching electrodeand moving element 120 (V_(CL)−V_(RS)) which produces the electrostaticforce is not critical at this time, and may be altered withoutsubstantially affecting operation of the actuator array.

As the moving element 120 of the selected element approaches thelatching electrode, the spring force exerted on it by bearing 150opposes its current direction of travel and grows in magnitude. At thistime, an electrostatic force attracting moving element 120 towards thelatching electrode is employed to achieve latching. Hence, successfullatching depends on the voltage between the latching electrode and themoving element 120 (V_(CL)−V_(RS)) being of sufficiently high magnitudeto overcome the spring force as well as any other opposing forces suchas friction or damping forces. On the other hand, any voltage appliedbetween the releasing electrode and moving element 120 (V_(CR)−V_(RS))at this time produces only a relatively small electrostatic forcepulling moving element 120 back towards the releasing electrode, sincemoving element 120 is relatively far from the releasing electrode.Hence, the voltage V_(CR)−V_(RS) is not critical at this time, and maybe altered without substantially affecting operation of the actuatorarray.

In the middle portion of axis 125, around the resting position of movingelement 120, both the spring force and the two electrostatic forces arerelatively low in magnitude. When the moving element 120 of the selectedelement is in this region, it remains in motion primarily due to themomentum it acquired since being released from its previous latchedposition.

In the embodiments described above, one or both of the first two of the“six conditions” described previously with reference to FIG. 4 can berelaxed as follows:|V _(RS) −V _(CR) |≦V _(R) (typically |V _(RS) −V _(CR)|=0V)  1.

-   -   during the early part of the movement only, i.e. during and        shortly after release.        |V _(RS) −V _(CL) |≦V _(L)  2.    -   in the latter part of the movement only, i.e. during and shortly        before latching.

These two conditions together with the unmodified conditions 3 to 6 ofthe original six conditions are referred to hereinafter as the “relaxedconditions”. Based on these relaxed conditions, the movement of a movingelement from one extreme position to the other (including its releasefrom the first extreme position and latching into the second extremeposition) can be split into two or more phases, such that at least oneof the selected R-voltage and the selected C-voltage varies betweenphases.

For example, the drive scheme described below, also referred tohereinafter as “drive scheme 6”, uses two phases, where the followingholds:

-   -   V_(RS) varies between phases as follows:        -   Phase 1: V_(RS)=V_(CR)        -   Phase 2: V_(RS)=0    -   V_(RU)=0 in both phases    -   V_(CR)≧V_(H) in both phases    -   V_(CL)=V_(CU)≧max(V_(L), 2×V_(H)) in both phases

This can be viewed as a variation on drive scheme 2, the differencesbeing that (a) the selected R-subset is selected only during Phase 1rather than throughout as in drive scheme 2; and (b) the latchingC-voltage V_(CL) and unselected C-voltage V_(CU) are lower than in drivescheme 2. This last point is an advantage of drive scheme 6 since itallows the controller circuit to be implemented more cost-effectivelycompared to drive scheme 2.

The frequency of the actuation clock (described previously withreference to FIG. 4) for drive scheme 6 is typically twice the actuationclock frequency for single-phase drive schemes such as drive schemes 1to 5 described previously, used with the same actuator array.

Subtracting V_(H) from all R-wire, A-wire and B-wire voltages in drivescheme 6 yields an electrically equivalent scheme referred tohereinafter as “drive scheme 7” characterized by:

-   -   V_(RS) varies between phases as follows:        -   Phase 1: V_(RS)=0        -   Phase 2: V_(RS)=V_(RU)    -   V_(RU)≦−V_(H) in both phases    -   V_(CR)=0 in both phases    -   V_(CL)=V_(CL)≧max(V_(L), −2×V_(RU))+V_(RU) in both phases

Drive scheme 7 has the advantage that the highest magnitude of drivevoltage (in this case, V_(CL)/V_(CU)) is lower than in all other driveschemes described so far. However, it also has the disadvantage ofemploying both positive and negative drive voltages.

FIG. 10 is a simplified representation of an actuator array inaccordance with certain embodiments of the invention, comprising eightactuator elements partitioned into four R-subsets and two C-subsets,analogously to the actuator arrays shown in FIGS. 4 to 7. R-wires arelabeled R0 to R3, A-wires A0 to A1 and B-wires B0 to B1. Each squarerepresents one actuator element 110. The actuator element located at theintersection of R-subset 1 and C-subset 1, also referred to hereinafteras the “selected element” and labeled 111, is currently latched in theA-position and is to be moved into the B-position.

The actuator array operates according to a drive scheme referred tohereinafter as “drive scheme 8”, which uses two drive voltages ofopposite polarities, a positive drive voltage +V_(D) and a negativedrive voltage −V_(D). The magnitude of both drive voltages is the largerof the hold voltage V_(H) and half of the latching voltage V_(L) (i.e.V_(D)=max(V_(L)/2, V_(H))). Drive scheme 8 is further characterized by:

-   -   V_(RS) varies between phases as follows:        -   Phase 1: V_(RS)=0V        -   Phase 2: V_(RS)=−V_(D)    -   V_(RU)=−V_(D) in both phases    -   V_(CR)=0V in both phases    -   V_(CL)=V_(CU)=+V_(D) in both phases

Within each square in FIG. 10, the top line refers to the magnitude ofV_(A) and the bottom line to the magnitude of V_(B). It can be seen thatthis drive scheme fulfills the “relaxed conditions” described above withreference to FIG. 9, and furthermore, offers some or all of thefollowing advantages over drive schemes described so far:

-   -   Since +V_(D) and −V_(D) have the same magnitude, one can be        generated from the other using a relatively simple and low-cost        circuit such as an inverting charge pump; whereas in other drive        schemes discussed so far, drive voltages generally differ in        magnitude and hence, generating drive voltages for these drive        schemes would normally employ a more complex and expensive        circuit such as a switched-mode DC-to-DC converter.    -   If V_(H)<V_(L)/2, then the highest magnitude of drive voltage        employed (in this case, V_(CL)/V_(CU)) is lower than in all        other drive schemes described so far.

Drive scheme 8 is not equivalent to drive schemes 6 and 7. For example:

-   -   For unselected elements located at the intersection of selected        C-wires and unselected R-wires and latched at the releasing        side, the V_(A) and V_(B) used to hold their moving elements in        their current position differs between drive schemes 6/7 and        drive scheme 8, during both phases.    -   For unselected elements located at the intersection of        unselected C-wires and unselected R-wires, the V_(A) and V_(B)        used to hold their moving elements in their current position        differs between drive schemes 6/7 and drive scheme 8, during        phase 1 only.    -   For selected elements, the voltage between the latching wire and        their moving elements differs between drive schemes 6/7 and        drive scheme 8, during phase 1 only.    -   For selected elements, the voltage between the releasing wire        and their moving elements differs between drive schemes 6/7 and        drive scheme 8, during phase 2 only.

The drive schemes above may assume that, at any given time during normaloperation, the controller either moves one or more actuator elementsfrom the A-position to the B-position, or moves one or more actuatorelements from the B-position to the A-position, or does not move anyactuator elements. However, with drive scheme 8 it is also possible tosimultaneously move one or more actuator elements from the A-position tothe B-position, while also moving one or more actuator elements from theB-position to the A-position, under the following conditions:

-   -   All actuator elements to be moved are located in selected        R-subsets, since moving elements can only be released if the        respective R-subset is selected; and    -   Actuator elements to be moved from their A-position to their        B-position cannot be located in the same C-subset as actuator        elements to be moved from their B-position to their A-position.        This is because, under drive scheme 8, the latching C-voltage        (V_(CL)=+V_(D)) differs from the releasing C-voltage        (V_(CR)=0V), making it impossible for a single A-wire or B-wire        to be both a latching wire and a releasing wire at the same        time.

In summary, under drive scheme 8 it is possible to simultaneously moveactuator elements in opposite directions, if they are all in the sameR-subset but in different C-subsets.

As described previously with reference to drive schemes 3 and 6, addingor subtracting a given voltage from all R-wire, A-wire and B-wirevoltages results in drive schemes that are equivalent to drive scheme 8.For example, adding V_(D) to all R-wire, A-wire and B-wire voltagesyields a variation referred to hereinafter as “drive scheme 9”characterized by

-   -   V_(RS) varies between phases as follows:        -   Phase 1: V_(RS)=V_(D)        -   Phase 2: V_(RS)=0V    -   V_(RU)=0V in both phases    -   V_(CR)=V_(D) in both phases    -   V_(CL)=V_(CU)=2×V_(D) in both phases

Drive scheme 9 eliminates negative voltages from the controller, which,depending on the technology used to implement the controller, may reduceits cost. Since the higher drive voltage 2×V_(D) is exactly double themagnitude of the lower drive voltage V_(D), it becomes possible togenerate the higher drive voltage from the lower one using a relativelysimple and low-cost circuit such as a voltage-doubling charge pump;whereas other drive schemes discussed so far do not generally have a 2:1ratio between drive voltages and hence, generating drive voltages forthese drive schemes would normally employ a more complex and expensivecircuit such as a switched-mode DC-to-DC converter. Depending on thetechnology used to implement the controller circuit, the use of adoubling charge pump may reduce or increase the cost of the controllercompared to using an inverting charge pump as with drive scheme 8.

It is appreciated that drive scheme 8, like all other drive schemesdiscussed here, can be used with actuator arrays of any size (i.e. anynumber of R-subsets and C-subsets, and any number of actuator elementsat each intersection of an R-subset and a C-subset). The small number ofR-subsets and C-subsets in FIGS. 2 to 7 and 10 have been chosen merelyfor simplicity. In practice, a 4×2 matrix of actuator elements as shownin FIG. 10 does not reduce the number of electrical connections betweenthe actuator array and controller 50 compared to an implementation withdedicated connections for each moving element and two shared connectionsfor all A-electrodes and all B-electrodes respectively; and hence thereis no advantage in building such a matrix. However for larger arraydimensions the number of connections is reduced dramatically (fromNrNc+2 to Nr+2×Nc). It is also appreciated that the polarity of drivevoltages in drive schemes 6 to 9 may be inverted without affectingoperation of the actuator array, as previously described with referenceto drive schemes 4 and 5. Furthermore, it is appreciated that driveschemes with more than two phases can be devised which will also fulfillthe “relaxed conditions” described above with reference to FIG. 9.

In drive schemes 1 to 9, the time for releasing a moving element fromone extreme position and latching it in the opposite extreme position,also referred to hereinafter as the actuation time T_(a), is determinedprimarily by the mass of moving element 120 and the spring force exertedon it by bearing 150, and is approximately equal to half the resonanceperiod T_(res) of moving elements 120, where T_(res) is the inverse oftheir mechanical resonance frequency described previously with referenceto FIG. 1B. This may limit the suitability of the apparatus for specificpurposes; for example, if the apparatus is used to produce sound orultrasound waves then the actuation time T_(a) is typically shorter thanhalf the period of the highest sound or ultrasound frequency to begenerated (according to the Nyquist sampling theorem). Furthermore,where oversampling is used (for example, in a noise-shaping loop such asthat described below with reference to FIGS. 27 to 29), it is desirableto minimize the actuation time in order to increase the oversamplingratio. One way to reduce actuation time is to reduce the mass of movingelement 120; however, application-specific requirements for mechanicalstability and reliability may limit how far this weight can be reduced.Another option is to increase the spring coefficient of bearing 150, butthis has the disadvantage of increasing the magnitude of the drivevoltages employed.

For actuator arrays controlled using multi-phase drive schemes, such asdrive schemes 6 to 9, an alternative approach to this problem is tooverlap phases. For example, drive scheme 8 allows for the simultaneousmovement of two sets of actuator elements, such that a first set ofactuator elements is in Phase 1 as described above, while a second setof actuator elements is in Phase 2; a process also referred tohereinafter as “double-speed addressing”. Although it does not affectthe overall time to complete each movement, double-speed addressingdoubles the number of opportunities per time unit for releasing movingelements. As a result, the physical effect produced by the actuatorarray can be controlled more accurately in time. For example, if theactuator array produces sound or ultrasound waves then the maximumfrequency that can be produced is doubled; and if oversampling is used,the oversampling ratio is effectively doubled. The effect is similar toreducing the actuation time T_(a) from T_(res)/2 to T_(res)/4, butwithout any change in the mechanical properties of actuator elements.However, whenever two elements are simultaneously in motion such thatone is in Phase 1 and the other in Phase 2, two conditions, referred tohereinafter as the “double-speed rules”, hold:

-   -   1. The two elements cannot be in the same R-subset, because        drive scheme 8 applies different voltages to selected R-wires in        each phase (0V in Phase 1 versus −V_(D) in Phase 2 and for        unselected R-wires).    -   2. If the two elements are moving in opposite directions, they        are in different C-subsets. This is because drive scheme 8        applies different voltages to releasing and latching wires (0V        for releasing wires versus +V_(D) for latching wires, in both        phases).

The second double-speed rule can be removed using a modified drivescheme, also referred to hereinafter as “drive scheme 10”, which ischaracterized by:

-   -   V_(RS) varies between phases as follows:        -   Phase 1: V_(RS)=0V        -   Phase 2: V_(RS)=−V_(D)    -   V_(RU)=−V_(D) in both phases    -   V_(CR) varies between phases as follows:        -   Phase 1: V_(CR)=0V        -   Phase 2: V_(CR)=+V_(D)    -   V_(CL)=V_(CU)=+V_(D) in both phases

Drive scheme 10 differs from drive scheme 8 in that the releasingC-voltage in Phase 2 is +V_(D) rather than 0V, which is the same as thelatching C-voltage in Phase 2. As a result, it becomes possible for anA-wire or B-wire to be the releasing wire for a moving element which isin Phase 1, while simultaneously acting as the latching wire for anothermoving element which is in Phase 2. However, this drive scheme mayemploy slightly higher drive voltages to ensure successful latching,and/or may slightly increase the time for latching under otherwiseidentical conditions.

FIG. 11 is a summary of drive schemes 6 to 10 in tabular form.

FIG. 12 is a summary of some further possible two-phase drive schemes.These are obtained by combining three different options (0, +V_(D) and“don't care”, i.e. either 0 or +VD) for V_(CR) in phase 2 with the samethree options for V_(CL) in phase 1, yielding a total of nine possiblecombinations, of which seven are shown in FIG. 12 (the remaining twocombinations being drive schemes 8 and 10 which are shown in FIG. 11).Each drive scheme results in a different set of “double-speed rules”(described previously for drive schemes 8 and 10). Some of the driveschemes shown may employ a slight adjustment of V_(D) to ensuresuccessful release and latching.

Drive schemes containing “don't care” conditions such as drive schemes11, 14, 15, 16 and 17, where one or both of V_(CR) and V_(CL) may beeither 0 or +V_(D) in the same phase, offer more degrees of freedom inselecting R-wire, A-wire and B-wire voltages to produce a desiredphysical effect. As a result, such drive schemes may enable moreaccurate production of the desired physical effect, and/or may simplifythe process of determining the R-wire, A-wire and B-wire voltages.However, the physical effect produced by actuator elements under suchdrive schemes may vary slightly depending on whether the respectivevoltage is 0 or +V_(D). Depending on the application, this variation mayor may not represent a disadvantage outweighing the advantage of higheraccuracy.

“Double-speed addressing” has been described previously with referenceto FIG. 10. In some embodiments, the method may be extrapolated, e.g. toachieve higher-than-double speed addressing, and generalized to triple,quadruple, or k-tuple speed addressing. k-tuple speed addressing inaccordance with certain embodiments of the present invention uses adrive scheme with k phases (where k is a positive integer), and anactuation clock k times faster than for a single-phase drive scheme withthe same actuator array, to effect movement of a moving element from oneof its extreme positions to the opposite extreme position. Potentiallyuseful drive schemes derived from drive scheme 8 share some or all ofthe following features:

-   -   V_(RS)=0 in the first phase and −V_(D) in the last phase.    -   V_(RU)=−V_(D) in all phases.    -   V_(CR)=0 in the first phase.    -   V_(CL)=+V_(D) in the last phase.    -   V_(CU)=+V_(D) in all phases.        Differences between these drive schemes include one or more of:    -   the value of V_(RS) in intermediate phases (i.e. any phases        which are neither the first nor the last); possible values        include 0, −V_(D) and “don't care” (i.e. either 0 or −V_(D))    -   the value of V_(CR) in phases other than the first phase;        possible values include 0, +V_(D) and “don't care” (i.e. either        0 or +V_(D))    -   the value of V_(CL) in phases other than the last phase;        possible values include 0, +V_(D) and “don't care” (i.e. either        0 or +V_(D))

As an example, one possible quadruple-speed drive scheme, referred tohereinafter as “drive scheme 18”, is characterized by:

-   -   V_(RS) varies between phases as follows:        -   Phases 1 and 2: V_(RS)=0V        -   Phases 3 and 4: V_(RS)=−V_(D)    -   V_(RU)=−V_(D) in all phases    -   V_(CR) varies between phases as follows:        -   Phases 1 to 3: V_(CR)=0V        -   Phase 4: V_(CR)=0V or +V_(D) (“don't care”)    -   V_(CR) varies between phases as follows:        -   Phase 1: V_(CR)=0V or +V_(D) (“don't care”)        -   Phase 4: V_(CR)=+VD    -   V_(CU)=+V_(D) in all phases

As described previously with reference to FIG. 10, the key advantage ofhigher-speed addressing is that the physical effect produced by theactuator array can be controlled more accurately in time. On the otherhand, higher-speed addressing also complicates the process ofdetermining R-wire, A-wire and B-wire voltages to produce a desiredphysical effect (referred to hereinafter as an “addressing method”).With double-speed or higher-speed addressing methods, the R-wire, A-wireand B-wire voltages for each actuation clock cycle are typically chosensuch that any moving elements released in previous actuation lockcycles, bit not yet latched in their new position, are correctlylatched; whereas with single-speed addressing methods, there is no suchconstraint on the selection of R-wire, A-wire and B-wire voltages, sinceall movements are completed within a single actuation clock cycle. As aresult, double-speed or higher-speed addressing methods typically havefewer degrees of freedom available at each actuation clock cycle tomprodice the desired physical effect. Depending on the application, thispotential disadvantage may or may not outweigh the advantage ofhigher-speed addressing.

It is appreciated that adding or subtracting any given voltage from alldrive voltages in any higher-speed drive scheme, or inverting thepolarity of all drive voltages, results in drive schemes that areelectrically equivalent to the original drive scheme. Furthermore, it isappreciated that higher-speed drive schemes may also be devised usingasymmetric drive voltages (for example, as a higher-speed version ofdrive schemes 6 or 7 presented previously), or using more than twononzero drive voltages (for example, as a higher-speed version of drivescheme 1 presented previously).

FIG. 13 is a graph of voltage waveforms for initialization of one ormore actuator elements in an actuator array using the previouslydescribed drive scheme 8, and the resulting deflection of moving element120 from its resting position.

“Initialization” herein refers to a process of latching some or allactuator elements within an array of electrostatic actuators, such asthose described previously with reference to FIGS. 2 to 4, into one oftheir extreme positions, for example, immediately after power-up. Sincemoving elements are in equilibrium at their resting position when theapparatus is powered down, the initialization process typically achieveslatching from the resting position; whereas during normal operation,moving elements are always latched into a new extreme position afterhaving been previously latched in, and then released from, the oppositeextreme position. The latching voltage V_(L) defined previously withreference to FIG. 3 is sufficient only to achieve latching in the lattercase but not from the resting position. As a result, the above driveschemes, which typically generate a voltage equal to V_(L) betweenmoving elements and latching electrodes, are not necessarily capable oflatching moving elements directly from their resting positions; this istypically first achieved in a separate initialization procedure beforethese drive schemes can be used.

One possible solution is to increase the magnitude of the selectedR-voltage and/or the latching C-voltage such that the magnitude of theresulting voltage between latching electrodes and moving elementsbecomes sufficiently large to latch moving elements directly from theirresting positions. However higher drive voltages may make the controllercircuit more costly to implement and/or increase the power consumptionof the apparatus during normal operation. Another possible solution isto use higher drive voltages for initialization only and revert to lowerdrive voltages for normal operation. However, the additional voltagesmay add complexity to the controller. For example, a controlleroperating according to drive scheme 8 is typically only capable ofapplying one of two drive voltages (0 or −V_(D)) to each R-wire and oneof two drive voltages (0 or +V_(D)) to each A-wire and B-wire, whereas amodified version with additional higher drive voltages would have toswitch R-wires and/or A-wires and B-wires between three differentvoltages.

The initialization procedure illustrated in FIG. 13 takes advantage ofthe moving elements' mechanical resonance and as a result, does notemploy higher or additional drive voltages. In FIG. 13, T_(Res) refersto the resonance period of moving elements 120, i.e. the inverse oftheir mechanical resonance frequency described previously with referenceto FIG. 1B; V_(CSA) refers to the voltage applied to selected A-wires,i.e. A-wires of C-subsets containing actuator elements to beinitialized; likewise, V_(CSB) refers to the voltage applied to selectedB-wires; and V_(RS) refers to the voltage applied to selected R-wires,i.e. those of R-subsets containing actuator elements to be initialized.In the bottom part of the graph, the deflection of a typical movingelement 120 away from its resting position and towards the A-position isplotted over time.

The initialization procedure illustrated in FIG. 13 typically comprisesfirst and second phases. In the first phase, the controller applies avoltage of 0V to selected R-wires, and the negative drive voltage −V_(D)to any other R-wires, also referred to hereinafter as unselected R-wires(i.e. V_(RS)=0, V_(RU)=−V_(D)). At the same time, the controlleralternately sets V_(CSA) and V_(CSB) to the positive drive voltage+V_(D) and 0V respectively, switching between these voltagesperiodically such that whenever +V_(D) is applied to a selected A-wire,0V is applied to the respective B-wire and vice versa, creating twosquare waves whose frequency is substantially equal to the mechanicalresonance frequency described with reference to FIG. 1B of movingelements 120, and which are 180 degrees out of phase; while alsoconstantly applying the positive drive voltage +V_(D) to any otherA-wires and B-wires. This causes moving element 120 to oscillate aroundits resting position, with the amplitude of the oscillation graduallyincreasing over time. In certain embodiments, the duration of this firstphase is substantially equal to an integer multiple of half theresonance period T_(res) of moving element 120, plus one quarter of theresonance period (i.e. T_(phase)≈(0.5×Ni+0.25)×T_(res), where Ni is aninteger), and just sufficiently long to allow maximum oscillationamplitude to be reached. Thus, at the end of the first phase, the movingelement 120 is near its resting position and travelling towards one ofthe two electrodes (in the case of FIG. 13, towards the A-electrode). Inthe simulated example shown in FIG. 13, the duration of the first phaseis six and a quarter resonance periods, i.e. Ni=12. However, it isappreciated that the optimum Ni depends on mechanical properties anddamping of the actuator element. In the second phase of theinitialization procedure, the controller applies the negative drivevoltage −V_(D) to all R-wires including selected R-wires, while keepingall A-wires and B-wires constantly at the same voltage applied to themat the end of the first phase.

The change in V_(RS) from the first phase to the second increases thevoltage between moving element 120 and the latching electrode (i.e. theelectrode towards which it is travelling) such that the resultingelectrostatic force combined with the moving element's momentum issufficient to overcome the spring force exerted by bearing 150, allowingmoving element 120 to reach a position close enough to the latchingelectrode to achieve latching into one of the two extreme positions asdescribed with reference to FIG. 1B (in the case of FIG. 13, theA-position). The duration of this second phase is typically sufficientto achieve latching, typically between half a resonance period and afull resonance period. For an initialization procedure to latch movingelements into the B-position rather than the A-position, the procedureis as described above, with the waveforms for V_(CSA) and V_(CSB)reversed. It is also possible latch moving elements of some C-subsetsinto the A-position and those of other C-subsets into the B-positionsimultaneously in a single initialization, by applying differentwaveforms different waveforms to the respective A-wires and B-wires.

Similar initialization procedures can be devised for other drive schemesdescribed previously. For example, adding V_(D) to all R-wire, A-wireand B-wire voltages yields an initialization procedure using only thedrive voltages already present in drive scheme 9.

It is appreciated that there need not be any unselected R-subsets orC-subsets during initialization; if all moving elements within theactuator array have substantially the same mechanical resonancefrequency, the entire array can be initialized at the same time. On theother hand, in an actuator array where mechanical resonance frequenciesvary substantially, the initialization procedure may be repeated severaltimes with signal timing adjusted to the different mechanical resonancefrequencies. It is also appreciated that the initialization procedurecan also be used at times other than after power-up, for example, inorder to return to a well-defined position any moving elements which maypreviously have failed to latch, for example, as a result of unusuallystrong mechanical shock.

FIG. 14 is a simplified block diagram of one embodiment of the presentinvention, comprising a controller 50 and actuator array 100. Thisparticular embodiment relies on the assumption that the physical effectproduced by the moving elements within the actuator array 100 isdetermined primarily by the number of moving elements in each extremeposition at any point in time, and that variations in the physicaleffect depending on which particular moving elements are in each extremeposition are either negligible or not relevant to the application wherethe apparatus is used; or alternatively, that the physical effect isdetermined primarily by the number of moving elements moving from oneextreme position to the other at any point in time, regardless of whichparticular moving elements execute the movement. The latter is true, forexample, where the physical effect produced by an individual actuatorelement is a pressure pulse, the overall physical effect produced by theentire apparatus is audible sound, and the physical size of the actuatorarray is significantly smaller than the wavelength of the highest audiofrequencies being reproduced (with larger or more widely spaced actuatorarrays, the resulting audible sound may be directional, as described inWO2007/135678 (“Direct digital speaker apparatus having a desireddirectivity pattern”)). In that case, the entire apparatus isessentially a digital-to-analog converter (DAC) whose analog output issound pressure (rather than voltage or current, like most DACs).

The controller 50 receives a digital audio signal 600 which is sampledperiodically, and adjusts the voltages applied to R-wires 400, A-wires410 and B-wires 420, causing the actuator elements within actuator array100 to move between their two extreme positions and thereby reproduce anaudible sound represented by audio signal 70. In this particularembodiment, the controller 50 comprises a low-pass filter 510, asample-rate converter 520, a scaler 530, a quantizer 540, an elementselector 550, and a high-voltage driver 560 e.g. as described below.

The low-pass filter (LPF) 510 receives digital audio signal 600 andproduces a low-pass filtered signal 610. The purpose of the LPF isvolume control. LPFs are well known in the art, but are not generallyused for volume control in sound reproduction systems based onconventional loudspeakers. In sound reproduction systems based onactuator arrays, however, using an LPF rather than conventional methodsfor volume control can be advantageous because it can result in improvedbass response at low volumes. This is described in detail inWO2007/135679 (“Systems and Methods for Volume Control in Direct DigitalSpeakers”).

The LPF is optional and may be omitted if there is no need for volumecontrol, or if volume control is to be effected by conventional methodsdespite the disadvantage of poorer bass response at low volumes.Alternatively, the LPF may be implemented in another part of a largersystem into which the entire apparatus is embedded; for example, it mayrun as a signal-processing algorithm in a multimedia processor IC(integrated circuit) in a consumer electronics device. As described inPublished PCT Application WO2007/135679 (“Systems and Methods for VolumeControl in Direct Digital Speakers”), the LPF typically has a slope of 6dB/octave above its corner frequency. Other characteristics of the LPFdescribed in the above-referenced application are not critical to theinvention.

The sample rate converter (SRC) 520 matches the sample rate of thelow-pass filtered signal 610 to the actuation clock frequency at whichelement selector 550 operates, producing a resampled signal 620. Thesample rate of the digital audio signal 600 and thus of the low-passfiltered signal 610 depends on the application. For example, digitaltelephony typically uses sample rates of 8 kHz or 16 kHz, whereascommonly used sample rates for digital music reproduction in consumeraudio devices include 44.1 kHz and 48 kHz. The actuation clockfrequency, on the other hand, is dictated by the mechanical propertiesof the actuator elements and the number of phases used in the drivescheme (k), as described previously with reference to FIGS. 4, 9 and 12,and is typically not equal to (typically higher than) typical samplerates for digital audio content, therefore sample rate conversion isemployed. Sample rate conversion is well known in the art, andimplementation details while they may affect overall sound fidelity ofthe apparatus, are not critical. The SRC is optional and may be omittedif the audio signal 600 is delivered to the controller 50 at a samplerate that equals the actuation clock rate. It may also be implemented inanother part of a larger system into which the entire apparatus isembedded.

The scaler 530 matches the range of the resampled signal 620 to theresolution of the actuator array 100, producing a scaled signal 630which directly represents the number of actuator elements that should bein the A-position (or alternatively, the number of elements that shouldbe in the B-position at any given time in order to produce the desiredsound. For example, the digital audio signal may be in two's complementformat with 16-bit resolution, such that its value can vary between−32768 and +32767. The range of actuator array 100, on the other hand,is equal to the number of actuator elements it contains, plus one. Forexample, in an actuator array with 32 R-subsets and 32 C-subsets,containing 1024 actuator elements, the number of moving elements in theA-position can take 1025 different values (from 0 to 1024; likewise forthe B-position). The range of the actuator array is typically lower thanthat of the resampled signal, therefore scaling is employed. Scaling istypically achieved by multiplying the resampled signal with a firstconstant and adding a second constant. In the example above, the firstconstant may be 1/64 and the second constant 512. The scaler is optionaland may be omitted if the ranges of resampled signal 620 and actuatorarray 100 match.

The quantizer 540 quantizes the scaled signal 630, taking account of thefact that the number of moving elements in the A-state (or B-state) isalways an integer. Its output is a quantized signal 640, which takesonly integer values. Quantization is well known in the art. Thequantized signal may, for example, be a truncated version of the scaledsignal 630, discarding the fractional part. Alternatively, the quantizermay use dithering, to improve performance of the apparatus. Dithering iswell known in the art, and is commonly used, inter alia, in analog-todigital and digital-to-analog converters. Dithering may be achieved, forexample, by adding a pseudo-random signal with a rectangular ortriangular probability distribution function (PDF) to the scaled signal630 before truncation. The quantizer is optional and may be omitted, forexample, if the resolution of the resampled signal 620 is less than orequal to that of actuator array 100.

The element selector 550 receives the quantized signal 640 anddetermines from it the array drive signals 650, indicating which of thedrive voltages is to be applied to each R-wire, A-wire and B-wire at anypoint in time in order to make the number of actuator elements in theA-position (or alternatively, the number of elements in the B-position)equal to, or as close as possible to, the number represented by thequantized signal 640. Methods for moving one or more specific actuatorelements between their two extreme positions, i.e. drive schemes, havebeen described previously with reference to FIGS. 4 to 12. Depending onthe state of each actuator element and on the quantized signal at anygiven time, there may be more than one way of obtaining the desirednumber of moving elements in the A-position (or in the B-position).Hence, various different element selection methods may be employed todetermine which specific actuator elements to select at any given pointin time. Element selection methods are described below with reference toFIGS. 15 to 24.

The high-voltage driver 560 translates the voltage levels of drivesignals 650 to the drive voltages employed by the actuator array 100under whichever drive scheme is used, and applies these drive voltagesto R-wires 400, A-wires 410 and B-wires 420. The high-voltage driver maybe implemented, for example, as a plurality of conventionallevel-shifting circuits. Depending on the mechanical dimensions ofactuator elements, drive voltages may have magnitudes of tens orhundreds of volts, whereas digital electronic circuits typically usesupply voltages well below 10 volts. Furthermore, all drive schemesdescribed above with reference to FIGS. 5 to 12 employ at least threedifferent drive voltages (for example, drive scheme 8 described withreference to FIG. 10 has +V_(D) and 0 for A-wires and B-wires, and−V_(D) and 0 for R-wires), whereas digital circuitry generally uses onlytwo distinct levels (logic high/low). For example, if drive scheme 8 isused, “high” and “low” outputs from the element selector 550 may betranslated to −V_(D) and 0 respectively for R-wires, and to +V_(D) and 0respectively for A-wires and B-wires. Therefore, level shifting isemployed. Level shifting circuits are known in the art.

It is understood that the functions of low-pass filtering, sample rateconversion and scaling need not be performed in the order shown in FIG.14, and may be performed in any order without affecting thefunctionality of the apparatus. Furthermore, the components of FIG. 14may be physically partitioned in different ways. For example, andwithout limitation, each of the LPF, SRC, quantizer and element selectormay be implemented as an algorithm running on a general-purposemicroprocessor or microcontroller or on a digital signal processor(DSP), or as a hard-wired electronic circuit. Any electronic circuitsforming part of the controller 50 may or may not be integrated into oneor more integrated circuits (ICs), and may be co-packaged with actuatorarray 100, with other system components, or implemented as a standalonecomponent.

FIGS. 15 to 23 are simplified flowchart illustrations of processestogether forming an element selection method which may be used in anelement selector in an apparatus such as that of FIG. 14. The elementselection method of FIGS. 15 to 23 is based on the previously describeddrive scheme 8, i.e. it assumes that movements of moving elements fromone extreme position to the other are completed within 2 actuation clockcycles. It is appreciated that mutatis mutandis, other drive schemes mayalternatively be used as a basis.

The method of FIG. 15 typically comprises some or all of the followingsteps, suitably ordered e.g. as shown:

-   -   Step 1510: Perform initialization procedure as described with        reference to FIG. 13, leaving some (typically half) of all        C-subsets with all their moving elements in the A-position        (“full”), and the other C-subsets with all their elements in the        B-position (“empty”). The initialization procedure finishes with        all R-signals, A-signals and B-signals “off”.    -   Step 1520: Choose a number d (e.g. any arbitrary number) such        that there exists an R-subset numbered d.    -   Step 1530: Choose a number e (e.g. any arbitrary number) such        that the C-subsets numbered e is empty.    -   Step 1540: Choose a number f (e.g. any arbitrary number) such        that there exists an R-subset numbered f.    -   Step 1550: Choose a number g (e.g. any arbitrary number) such        that the C-subset numbered g is full.    -   Step 1560: Initialize internal variable Na to the number of        moving elements currently in the A-position    -   Step 1570: Execute main loop (e.g. as per FIG. 16) once per        actuation clock cycle

The method of FIG. 16 typically comprises some or all of the followingsteps, suitably ordered e.g. as shown:

-   -   Step 1610: Compute the difference net_moves between the element        selector input signal (representing the number of moving        elements that should be in the A-position to produce the desired        physical effect) and the actual number of elements in the        A-position (internal variable Na)    -   Step 1620: If net_moves is zero perform method of FIG. 23    -   Step 1630: If net_moves is positive perform method of FIG. 17    -   Step 1640: If net_moves is negative perform method of FIG. 18    -   Step 1650: Return to step 1610 at the next actuation clock cycle

The method of FIG. 17 typically comprises some or all of the followingsteps, suitably ordered e.g. as shown:

-   -   Step 1710: If any A-signal, or any B-signal other than b(e) was        “on” during the last actuation clock cycle: see FIG. 23.    -   Step 1720: If no A-signal, nor any B-signal other than b(e) was        “on” during the last actuation clock cycle, perform some or all        of the following operations:    -   A: Turn b(e) “on”, and all other A-signals and B-signals “off”.    -   B: If any R-signal numbered between d and d+net_moves−1 was “on”        during the previous actuation clock cycle: perform method of        FIG. 18    -   C: If no R-signal numbered between d and d+net_moves−1 was “on”        during the previous actuation clock cycle: perform method of        FIG. 19    -   Step 1730: Increment Na by the number of R-signals that are        currently “on”    -   Step 1740: Jump to step 1650 in main loop (e.g. as per FIG. 16)

The method of FIG. 18 typically comprises some or all of the followingsteps, suitably ordered e.g. as shown:

-   -   Step 1810: Turn “on” any R-signals numbered from d up to and        including the lowest-numbered R-signal which was “off” during        the previous actuation clock cycle (if any).    -   Step 1820: Turn all other R-signals “off”    -   Step 1830: Increment d by the number of R-signals that are        currently “on”    -   Step 1840: Jump to step 1730 in FIG. 17

The method of FIG. 19 typically comprises some or all of the followingsteps, suitably ordered e.g. as shown:

-   -   Step 1910: If d+net_moves>Nr, perform some or all of the        following operations:    -   A: Turn “on” all R-signals numbered from d up to and including        Nr−1.    -   B: Turn all other R-signals “off”    -   C: Set d=0    -   D: If e=Nc−1, set e=0; otherwise increment e by one    -   Step 1920: If d+net_moves−1<Nr, perform some or all of the        following operations:    -   A: Turn “on” all R-signals numbered from d up to and including        d+net_moves−1.    -   B: Turn all other R-signals “off”    -   C: Increment d by net_moves.    -   Step 1930: Jump to step 1730 in FIG. 17

The method of FIG. 20 typically comprises some or all of the followingsteps, suitably ordered e.g. as shown:

-   -   Step 2010: If any B-signal, or any A-signal other than a(g) was        “on” during the last actuation clock cycle, perform method of        FIG. 23.    -   Step 2020: If no B-signal, nor any A-signal other than a(g) was        “on” during the last actuation clock cycle, perform some or all        of the following operations:    -   A: Turn A(g) “on”, and all other A-signals and B-signals “off”.    -   B: If any R-signal numbered between f and f−net_moves−1 was “on”        during the previous actuation clock cycle: perform method of        FIG. 21    -   C: If no R-signal numbered between f and f−net_moves−1 was “on”        during the previous actuation clock cycle: perform method of        FIG. 22    -   Step 2030: Decrement Na by the number of R-signals that are        currently “on”    -   Jump to step 1650 in main loop (FIG. 16)

The method of FIG. 21 typically comprises some or all of the followingsteps, suitably ordered e.g. as shown:

-   -   Step 2110: Turn “on” any R-signals numbered from f up to and        including the lowest-numbered R-signal which was “off” during        the previous actuation clock cycle (if any).    -   Step 2120: Turn “off” all other R-signals    -   Step 2130: Increment f by the number of R-signals that are        currently “on” step 2140: Jump to step 2030 in FIG. 20

The method of FIG. 22 typically comprises some or all of the followingsteps, suitably ordered e.g. as shown:

-   -   Step 2210: If f−net_moves>Nr:    -   A: Turn “on” all R-signals numbered from f up to and including        Nr−1.    -   B: Turn “off” all other R-signals    -   C: Set f=0    -   D: If g=Nc−1, set g=0; else increment g by one    -   Step 2220: If f−net_moves≦Nr, perform some or all of the        following operations:    -   A: Turn “on” all R-signals numbered from f up to and including        f−net_moves−1.    -   B: Turn “off” all other R-signals    -   C: Increment f by net_moves.    -   Step 2230: Jump to step 2030 in FIG. 20

The method of FIG. 23 typically comprises some or all of the followingsteps, suitably ordered e.g. as shown:

-   -   Step 2310: Turn “off” all R-signals    -   Step 2320: If Na was changed during the previous actuation clock        cycle, perform some or all of the following operations:    -   A: Keep “on” any A-signal or B-signal to which was “on” during        the previous actuation clock cycle.    -   B: Turn “off” all other A-signals and B-signals    -   Step 2330: If Na was not changed during the previous actuation        clock cycle, turn “off” all A-signals and all B-signals.    -   Step 2340: Return.

Generally, the element selection method of FIGS. 15 to 23 receives asingle input signal sampled in accordance with the actuation clock,which may for example be the output of a quantizer such as signal 640 inFIG. 14. For an actuator array with Nr R-subsets and Nc C-subsets, theelement selection method of FIGS. 15 to 23 assumes that each R-subsetcontains Nc moving elements and each C-subset contains Nr movingelements. The method produces Nr+2×Nc single-bit array drive signals: NrR-signals, numbered r0 to r(Nr−1) indicating the voltage to be appliedto each R-wire of the actuator array; Nc A-signals, numbered a0 toa(Nc−1) indicating the voltage to be applied to each A-wire; and NcB-signals, numbered b0 to b(Nc−1) indicating the voltage to be appliedto each A-wire. These may, for example be fed to a high-voltage driveras shown in FIG. 14. It is assumed that each of these signals controlsthe respective R-wire, A-wire and B-wire with the same number. When asignal is “on”, the voltage applied to the respective wire is 0V; whenit is “off”, that voltage is −VD (for R-wires) or +VD (for A-wires andB-wires).

The number of elements in the A-position at each actuation cycle in anactuator array controlled by the element selection method of FIGS. 15 to23 closely approximates the method's input signal if:

-   -   1. e never becomes equal to g (e and g are defined in FIG. 15),        and    -   2. the slew rate of the method's input signal is less than Nr/2        per actuation clock cycle.

If e and g become equal, the controller might apply 0V to both theA-wire and the B-wire of a single C-subset, which is disallowed underdrive scheme 8 because it would cause moving elements in that C-subsetto be released from one extreme position without being latched in theother extreme position. E and g can be prevented from becoming equal,for example, by ensuring that at least one C-subset is “full” (i.e. hasall its moving elements in the A-position) and at least one C-subset is“empty” (all moving elements in the B-position) at all times. In anapparatus as shown in FIG. 14, this may be achieved, for example, bydesigning the scaler 530 such that the value of quantizer output signal640 (i.e. the input to the element selection method of FIGS. 15 to 23)is always above Nr and below Nr×(Nc−1). Alternatively, the input signalmay be limited elsewhere, e.g. within an improved version of the elementselection method of FIGS. 15 to 23 itself.

The slew rate limitation of the element selection method of FIGS. 15 to23 accrues because the element selection method of FIGS. 15 to 23 neverreleases moving elements within more than one C-subset in the sameactuation clock cycle. As long as the input signal does not increase ordecrease by more than Nr/2 per actuation clock cycle, the number ofelements in the A-position, while not necessarily exactly equal to theinput signal at every actuation clock cycle, still closely approximatesit. If the input signal changes faster, the difference between the inputsignal and the number of elements in the A-position (referred tohereinafter as “addressing error”) may accumulate over more than twoactuation clock cycles. In such cases, the element selection method ofFIGS. 15 to 23 enters a repetitive two-cycle pattern where, every othercycle, an entire C-subset of moving elements is released from an extremeposition, followed by a cycle where no moving elements are released andthe previously released ones are latched. Short bursts of this two-cyclepattern may also occur if the slew rate is below Nr/2 but close to it.

The element selection method of FIGS. 15 to 23 executes only a smallnumber of steps during each actuation clock cycle, and employs only asmall amount of memory. Its stored data comprises the variables d, e, f,g, Na, and the previous values of its own outputs, i.e. of array drivesignals r0 to r(Nr−1), a0 to a(Nc−1) and b0 to b(Nc−1). The elementselection method of FIGS. 15 to 23 does not keep track of the positionof each moving element individually, since this information is impliedby the internal variables d, e, f and g.

It is appreciated that element selection methods similar to the elementselection method of FIGS. 15 to 23 can also be devised for other driveschemes, such as drive schemes 1 to 7 and 9 to 18 described previously(logical supersets of drive scheme 8, e.g. drive schemes 11, 15 and 17,support the element selection method of FIGS. 15 to 23 as-is). Thecomplexity of such similar methods is a function of the number ofdifferent voltages, and of the number of phases (k) used in the drivescheme. Similar methods for use with single-phase drive schemes, such asdrive schemes 1 to 5 described previously, typically execute fewer stepsper actuation clock cycle than the element selection method of FIGS. 15to 23 because all moving elements released during one actuation clockcycle are already latched before the next actuation clock cycle begins.Conversely, similar methods for use with higher-speed drive schemes,such as for example the four-phase drive scheme 18, typically executemore steps per actuation clock cycle than the element selection methodof FIGS. 15 to 23, because under higher-speed drive schemes, the releaseof any moving elements during one actuation clock cycle creates arequirement to latch the released moving elements in the oppositeextreme position three actuation clock cycles later, requiring specificvoltages on certain R-wires, A-wires and B-wires and thereby reducingthe degrees of freedom available to the controller.

It is appreciated furthermore, that it is also possible, for any givendrive scheme, to devise element selection methods bearing no resemblanceto the element selection method of FIGS. 15 to 23. For example, a“brute-force” method may compute the position of each moving element atthe next clock cycle for every possible combination of array drivesignal values allowed by the drive scheme, and select an optimalcombination of array drive signal values according to criteria such asthe addressing error produced, and/or other criteria which may berelevant in a given application.

FIG. 24 is a simplified representation of an actuator array inaccordance with certain embodiments of the invention, comprising 64actuator elements partitioned into eight R-subsets and eight C-subsets,analogously to the actuator arrays shown in FIGS. 2 and 4. R-wires arelabeled R0 to R7, A-wires A0 to A7 and B-wires B0 to B7. Each squarerepresents one actuator element.

In FIG. 24, the actuator elements are numbered according to the formula:element number=number of R-subsets×C-subset number+R-subset numberand labeled in FIG. 24 in hexadecimal notation. Twenty-two movingelements, shaded in FIG. 24 and numbered 16 to 2B, are in the A-positionand the remaining moving elements, not shaded in FIG. 24, are in theB-position.

This is a typical situation for an actuator array controlled by theelement selection method of FIGS. 15 to 23. In this example, the valuesof internal variables in the element selection method of FIGS. 15 to 23are:

-   -   Na=22    -   d=4    -   e=5    -   f=6    -   g=2        It can be seen in FIG. 24 that the numbers of the set of moving        elements in the A-position (referred to hereinafter as the        “A-set”) form a continuous sequence, running from 16 to 2B (in        hexadecimal notation as per FIG. 24). Likewise, the numbers of        the set of moving elements in the B-position (referred to        hereinafter as the “B-set”) also form a continuous sequence,        running from 2C to 15, wrapping around from 3F (the        highest-numbered moving element) back to 00. The element        selection method of FIGS. 15 to 23 has the property that both        the A-set and the B-set always form such continuous sequences        which may or may not wrap around from the highest-numbered        moving element to the lowest-numbered one (referred to        hereinafter as a “continuous wraparound sequence”). The element        selection method of FIGS. 15 to 23 relies on this property to        keep track of the positions of the moving elements without        employing an Nr×Nc matrix data structure.

In the situation of FIG. 24, if the value of the input to the elementselection method of FIGS. 15 to 23 increases, the next moving elementsto be released from the B-position are 2C, 2D, 2E etc., in ascendingorder according to their numbering. Likewise, if the value of the inputto the element selection method of FIGS. 15 to 23 decreases, the nextmoving elements to be released from the A-position are 16, 17, 18 etc.,in descending order according to their numbering. In certainapplications, it may be undesirable for the element selection method toalways release moving elements in the same order, as is the case for theelement selection method of FIGS. 15 to 23. One reason for this ismismatch noise resulting from mismatch errors, i.e. differences in themagnitude of the physical effect produced by each moving element, whichmay result, for example, from manufacturing tolerances, or from movingelements being mechanically damaged at some time after theirmanufacture. If moving elements are always released in the same order,the spectrum of such mismatch noise (depending on the input signal) maybe such that mismatch noise energy is concentrated at certainfrequencies not contained in the input signal. This phenomenon is wellknown in sigma-delta digital-to-analog converters, and may cause audiblesound reproduced by such digital-to-analog converters to contain audibletones not present in the input signal. Various method are known in theart for shaping the frequency spectrum of mismatch noise to, forexample, make mismatch noise less audible or even inaudible in audioapplications. One such method, commonly referred to as “data-weightedaveraging” (DWA), distributes mismatch noise energy approximately evenlyacross the frequency spectrum, i.e. “whitens” it. An element selectionmethod according to certain embodiments of the present invention mayimplement DWA by releasing 2×net_moves moving elements from theA-position and net_moves moving elements from the B-position inactuation clock cycles where net_moves is positive, and releasing2×net_moves moving elements from the B-position and net_moves movingelements from the A-position in actuation clock cycles where net_movesis positive. However, due to the fact that that typically, electricalconnections are shared between actuator elements in actuator arrays,rather than each electrical connection being dedicated to one particularelement as is typically the case in conventional digital-to-analogconverters, such element selection methods implementing DWA may becomplex (i.e. execute a large number of steps at each actuation clockcycle), and/or the number of elements in the A-position at eachactuation cycle in an actuator array controlled by such an elementselection method may approximate the method's input signal less closelythan with element selection methods not implementing DWA.

Methods for “whitening” the frequency spectrum of mismatch noise, whichcan be used directly with the element selection method of FIGS. 15 to 23and methods based upon the element selection method of FIGS. 15 to 23,are now described. The method of FIGS. 15 to 23 assumes that each of theR-signals r0 to r(Nr−1), A-signals a0 to a(Nc−1) and B-signals b0 tob(Nc−1) controls the respective R-wire, A-wire or B-wire of the actuatorarray. However, if these assignments are altered such that, for example,R-signal r4 controls an R-wire other than R4, or A-signal a0 andB-signal b0 control an A-wire other than A0 and a B-wire other than B0respectively, then the order in which the element selection method ofFIGS. 15 to 23 releases moving elements is changed. By repeatedly (forexample, once per actuation clock cycle) making such changes to theassignment of array drive signals to R-wires, A-wires and B-wires, theorder in which moving elements are released becomes pseudo-random, thusdistributing mismatch noise energy more evenly across the frequencyspectrum.

In the following examples, R′(i) denotes the R-wire currently controlledby R-signal r(i), A′(i) denotes the A-wire currently controlled byA-signal a(i), and B′(i) denotes the B-wire currently controlled byB-signal b(i). In the situation depicted in FIG. 24, R-signals r4 and r5may be swapped, such that r4 controls R′5 (which in this case, is R5)and r5 controls R′4 (in this case, R4), without affecting the positionof any moving element in the actuator array. After swapping r4 and r5,the next moving element to be released from the B-position is 2D,whereas before the swap, it was 2C. Likewise, r6 and r7 may be swappedsuch that r6 controls R′7 and r7 controls R′6, resulting in movingelement 17, rather than 16, becoming the next moving element to bereleased from the A-position. Any two of R-signals r0 to r3 may also beswapped without affecting the position of any moving element in theactuator array. Overall, in the situation depicted in FIG. 24 there arethree sets of R-signals within which any member can be swapped with anyother: {r0,r1,r2,r3}, {r4,r5}, and {r6,r7}. However, swapping anyR-signal from one of these sets with any R-signal from another set maydisrupt the operation of the element selection method of FIGS. 15 to 23,resulting in the apparatus no longer producing the desired physicaleffect. A-signals and B-signals may be swapped analogously. For example,in the situation depicted in FIG. 24, A-signals a6 and a1 may be swappedby changing output assignments such that a6 controls A′1 (which in thiscase, is A1), and a1 controls A′6 (in this case, A6). Whenever twoA-signals are swapped, the respective B-signals are also swapped, e.g.in the case described above, output assignments are changed such that b6controls B′1 (in this case, B1), and b1 controls B′6 (in this case, B6).After this swap, the next element to be released from the B-position ina future actuation clock cycle, after C-subset 5 becomes full, is movingelement 08 in C-subset 1, rather than moving element 30 in C-subset 6.A-signals are not swapped with B-signals, i.e. A-signals always controlA-wires and B-signals always control B-wires. In the situation depictedin FIG. 24, there are two sets of A-signals whose members may be swappedwith each other without disrupting the operation of the elementselection method of FIGS. 15 to 23: {a0,a1,a6,a7} and {a3,a4}; andlikewise for B-signals. Neither of a2, a5, b2 or b5 can be swapped withany other C-subset without disrupting the operation of the elementselection method of FIGS. 15 to 23.

For sets of more than two R-signals that may be swapped, such as the set{r0,r1,r2,r3} in the example above, a controller according to certainembodiments of the present invention may select a pair of R-signals tobe swapped, for example, using a pseudo-random number generator.Alternatively, the assignment of r0, r1, r2 and r3 to R′0, R′1, R′2, andR′3 may be scrambled by any other method such that each of r0, r1, r2and r3 controls exactly one of the R-wires R′0, R′1, R′2, and R′3.Likewise, in the example above, the controller may select any pair ofA-signals within the set {a0,a1,a6,a7} and the respective pair ofB-signals for swapping, or it may change output assignments such thateach of a0, a1, a6 and a7 controls exactly one of the A-wires A′0, A′1,A′6 and A′7, and each respective B-output controls the respectiveB-wire.

Typically, any two R-signals r(i) and r(j) may be swapped if, for all mwhere 0≦m<Nc, the moving element at the intersection of the R-subset ofR-wire R′(i) and C-subset m is in the same position and moving in thesame direction (if in movement) as the moving element at theintersection of the R-subset of R′(j) and C-subset m.

Typically, any two A-signals a(i) and a(j) and respective B-signals b(i)and b(j) may be swapped if, for all m where 0≦m<Nr, the moving elementat the intersection of R-subset m and the C-subset of A-wire A′(i) andB-wire B′(i) is in the same position and moving in the same direction(if in movement) as the moving element at the intersection of R-subset mand the C-subset of A′(j) and B′(j).

With the element selection method of FIGS. 15 to 23, most C-subsets areeither full or empty during any given clock cycle. As a result, if theelement selection method of FIGS. 15 to 23 is used, any two A-signalsa(i) and a(j) and respective B-signals b(i) and b(j) may be swapped if(using brackets to indicate the precedence of logical operators): either(e<i<g and e<j<g), or ((i>e or i<g) and (j>e or j<g)).

Improvements to the element selection method of FIGS. 15 to 23 to reduceaddressing errors and improve transient response (e.g. enable thecontroller to release a larger number of moving elements at eachactuation clock cycle) are now described. In FIG. 24, the maximum numberof moving elements that the element selection method of FIGS. 15 to 23can release from the A-position during the current actuation clock cycleis two (the elements numbered 16 and 17 in FIG. 24). Thus, if net_movesexceeds two, the addressing error during the current actuation clockcycle will be nonzero. Likewise, the maximum number of moving elementsthat the element selection method of FIGS. 15 to 23 can release from theB-position within a single actuation clock cycle in the situation ofFIG. 24 is four (elements numbered 2C to 2F in FIG. 24), and thus,net_moves values below −4 will also produce nonzero addressing errors(of opposite polarity compared to the case where net_moves>2). In thesecases, the addressing errors are a direct consequence of the fact thatthe element selection method of FIGS. 15 to 23 never releases movingelements within more than one C-subset in the same actuation clockcycle. By using improved versions of the element selection method ofFIGS. 15 to 23 capable of releasing moving elements within more than oneC-subset during a single actuation clock cycle, addressing errors may beeliminated in such cases. For example, if net_moves=6, exactly sixmoving elements may be released from the B-position by skipping to thenext C-subset, applying 0V to B6 and to any six R-wires; or by applying0V to R2-R5, B5 and B6 (selecting eight moving elements but takingadvantage of the fact that moving elements 2A and 2B are already in theA-position). Alternatively, the same physical effect may be achieved byapplying 0V to R4-R7, A2, B5 and B6, thereby simultaneously releasingeight moving elements (2C-2F and 34-37) from the B-position and twomoving elements (16 and 17) from the A-position. Note however, thatapplying 0V to R0, R1, R4-R7, B5 and B6 would produce a differentphysical effect because a total of ten moving elements (2C-31 and 34-37)would be released, rather than six. Each of the possible solutionsdescribed above breaks the continuity of the A-set such that it nolonger forms a continuous wraparound sequence. As a result, elementselection methods which eliminate addressing errors in these situationsare typically more complex than the element selection method of FIGS. 15to 23. Such methods may, for example, split the A-set and B-set into Scontinuous wraparound sequences, and employ 4×S internal variablesanalogous to d, e, f and g of the element selection method of FIGS. 15to 23 to keep track of each continuous wraparound sequence.Alternatively, the number of continuous wraparound sequences may varyover time as appropriate to minimize addressing errors, or elementselection methods may be devised which keep track of the position ofeach actuator element irrespective of any continuous wraparoundsequences.

It is appreciated that situations may also occur where addressing errorsare not due to limitations of a particular element selection method, butrather are inevitable regardless of the element selection method used.For example, in the actuator array of FIG. 24, if all moving elementsare in the A-position, it is not possible to release exactly elevenmoving elements during a single actuation clock cycle; generally, if theactuator array has Nr R-subsets and Nc C-subsets, it is not possible torelease exactly P moving elements if P is a prime number larger thanboth Nr and Nc.

FIG. 25 shows the actuator array of FIG. 24, after the following arraydrive signals have been swapped e.g. as described with reference to FIG.24:

-   -   R-signals r4 and r5    -   R-signals r6 and r7    -   A-signals a1 and a6    -   B-signals b1 and b6

All moving elements are in the same position as in FIG. 24. However, inFIG. 25, the next six moving elements to be released from the B-positionare 2D, 2C, 2F, 2E, 08 and 09 (in this order), whereas in FIG. 24, thenext six moving elements to be released from the B-position are 2C, 2D,2E, 2F, 30 and 31.

Whereas in FIG. 24, R′(i) is R(i) for all i where 0≦i<Nr, and A′(j) isA(j) and B′(j) is B(j) for all j where 0≦j<Nc, this is no longer thecase in FIG. 25. When array drive signals are swapped periodically atevery actuation clock cycle, the assignment of array drive signals toR-wires, A-wires and B-wires becomes pseudo-random.

FIG. 26 shows the actuator array of FIG. 24, with many moving elementsin a different position compared to FIG. 24.

Unlike in FIG. 24, the number in each square of FIG. 26 is the virtualelement number of each moving element, defined in terms of the arraydrive signals currently controlling it:virtual element number=Nr×A-signal number+R-signal number

It can be seen in FIG. 26 that, although the element numbers of theA-set do not form a continuous wraparound sequence as described withreference to FIG. 24, the virtual element numbers of the A-set do form acontinuous wraparound sequence. Furthermore, the virtual element numbersof the A-set are the same in FIG. 26 as in FIG. 24. As a result, all theinternal variables of the element selection method of FIGS. 15 to 23 (d,e, f and g, described previously with reference to FIGS. 15 to 23), havethe same value in the situation of FIG. 26 and in that of FIG. 24. Ineffect, the two situations are identical as far as the operation of theelement selection method of FIGS. 15 to 23 is concerned.

FIG. 27 is a simplified block diagram of an apparatus according tocertain embodiments of the invention, comprising a controller 50 andactuator array 100. The controller 50 contains an element selector 550and a high-voltage driver 560, whose function is described above withreference to FIG. 14. In the absence of addressing errors, the number ofmoving elements within actuator array 100 that are in the A-positionequals the number represented by the input signal 601 of elementselector 550. Element selector 550 is placed inside a noise shaping loop60 which also comprises a loop filter 553, two adders 541 and 552, andan inverter (i.e. a digital multiplication by −1) 551. The elementselector 550 generates an additional signal 651 representing the numberof moving elements which actually are in the A-position (as opposed tosignal 601 which represents the number of moving elements that should bein the A-position to produce the desired physical effect). The adder 552and inverter 551 subtract this signal from the input signal 601 ofelement selector 550, generating an error signal 653 which representsthe addressing error introduced by element selector 550. The loop filter553 filters the error signal 652 and the resulting filtered error signal653 is added to the loop input signal 600 to generate the input signal601 for the element selector 550.

Assuming that the addressing error is not correlated with the inputsignal 600, the signal transfer function (STF) of the loop is one, whileits noise transfer function (NTF) is given by:NTF=1−H _(e) [z]where H_(e)[z] is the impulse response of loop filter 61 in thez-domain. By designing a loop filter with a suitable H_(e)[z], a NTF canbe obtained which has a high gain in a frequency band of interest(“in-band gain”) and a low gain outside this frequency band(“out-of-band gain”). As a result, the frequency spectrum of addressingnoise (resulting from addressing errors) is shaped such that thephysical effect produced by actuator array 100 contains less addressingnoise in the frequency band of interest resulting than it would withoutthe noise shaping loop 60.

Similar noise shaping loops are known in the art for shaping thefrequency spectrum of quantization noise, e.g. in digital-to-analogconverters (DACs) and analog-to-digital converters (ADCs), and arecommonly referred to as “sigma-delta modulators” and “delta-sigmamodulators”. Methods for designing loop filters for conventionalsigma-delta modulators are known in the art.

Design goals for loop filters, both in conventional sigma-deltamodulators and in addressing-noise shaping loops according to certainembodiments of the present invention, typically include obtaining adesired NTF, and ensuring that the noise-shaping loop is eitherunconditionally stable (i.e. not producing oscillations not present inthe input signal, which is generally undesirable), or stable underspecific conditions. Conventional methods for predicting the NTF as afunction of the loop filter's impulse response, or for finding a loopfilter response to approximate a desired NTF, may also be used foraddressing-noise shaping loops according to certain embodiments of thepresent invention.

However, conventional methods for predicting whether a conventionalsigma-delta modulator is stable, or for choosing the loop filter'simpulse response to ensure stability, are not necessarily suitable foraddressing-noise shaping loops according to certain embodiments of thepresent invention. The stability of addressing-noise shaping loopsaccording to certain embodiments of the present invention depends on theelement selection method used. For example, the element selection methodof FIGS. 15 to 23 described previously with reference to FIGS. 15 to 23enters a repetitive two-cycle pattern if the input signal has a highslew rate, producing oscillations at half the actuation clock frequency.Adding an addressing-noise shaping loop may cause such oscillations topersist longer than in a similar apparatus without a noise-shaping loop.As a result, addressing-noise shaping loops wherein the element selectoruses the element selection method of FIGS. 15 to 23 become unstablerelatively easily. With other element selection methods, such as thevariations on the element selection method of FIGS. 15 to 23 describedwith reference to FIG. 24, the loop may remain stable for a wider rangeof input signals.

Furthermore, the stability of addressing-noise shaping loops accordingto the present may also depend on the degree of correlation between theaddressing error and the input signal. As noted above, addressing-noiseshaping loops according to certain embodiments of the present inventionassume there is no such correlation. Likewise, conventional sigma-deltamodulators rely on an assumption that quantization error is notcorrelated with the input signal. In fact, both types of errorstypically exhibit a degree of correlation with the input signal. Bothconventional sigma-delta modulators and addressing-noise shaping loopsaccording to certain embodiments of the present invention assume therespective correlation to be low enough to be negligible. However,depending on the element selection method used, the degree ofcorrelation between addressing error and input signal in anaddressing-noise shaping loop according to certain embodiments of thepresent invention may be higher than the correlation betweenquantization noise and input signal in a conventional sigma-deltamodulator.

Generally, the stability of addressing-noise shaping loops according tocertain embodiments of the present invention depends on both the loopfilter's impulse response and the element selection method used. Forspecific input signals, loop stability may be verified by simulating theentire noise-shaping loop, e.g. in a software package such as MATLAB.For a given element selection method, the loop is more likely to bestable if the loop filter 553 has a short, smooth impulse response. Forexample, if the loop filter 553 is a finite impulse response (FIR)filter with a transfer function given in the z-domain as b0+b1 z^−1+b2z^−2+b3 z^−3+ . . . +b(n)z^−n, the loop is more likely to be stable if nis low and |b(i)−b(i+1)| is low for 0≦i<n. As an example, anaddressing-noise shaping loop according to certain embodiments of thepresent invention may be stable for a specific input signal when using aloop filter with the impulse response 0.5z^−1+0.5z^−2, and unstable forthe same input signal when using a loop filter with the impulse responsez^−1+0z^−2.

Various different topologies of noise shaping loops are known in theart. While the example of FIG. 27 shows a topology known as “errorfeedback”, this is an example only and any other loop topology may beused. Noise shaping loop topologies known in the art include, withoutlimitation: “single feedback”, topologies using feed-forward instead ofor in addition to feedback, cascaded and multi-stage topologies.

FIG. 27 assumes that the noise shaping loop 60 includes a delay of atleast one actuation clock cycle. For example, if the error signal 653does not already include a delay, and loop filter 553 is a finiteimpulse response (FIR) filter with a transfer function given in thez-domain as b0+b1 z^−1+b2 z^−2+b3 z^−3+ . . . +b(n)z^−n, then b0 istypically zero. Alternatively, the delay may be a natural by-product of,or a deliberate addition to, some or all of element selector 550,inverter 551, and/or adder 552.

The loop filter and hence NTF may be of any order and may have anycharacteristic, such as lowpass, bandpass or highpass.

The signal transfer function (STF) may be one. Alternatively, dependingon the application, a STF with non-flat frequency response may bedesirable, and/or its effect may be cancelled by other system componentswith a non-flat frequency response. Noise shaping loop architectureswith non-flat STFs are well known in the art.

In all text referring to FIG. 27 onward, the word “A-position” may bereplaced with “B-position” without fundamentally altering operation ofthe apparatus.

A controller according to certain embodiments of the present inventionmay include a noise-shaping loop as shown in FIG. 27 and subsequentFigures e.g. in conjunction with one or more of the low-pass filter,sample-rate converter, scaler and quantizer described with reference toFIG. 14.

FIG. 28 is a simplified block diagram of another embodiment of theinvention, analogous to that of FIG. 27, but with noise shaping appliedto quantization noise as well as addressing noise. The use of aquantizer within the present invention has been described previouslywith reference to FIG. 14. Quantization noise, or quantization error,refers to the difference between the quantizer's input and its output.In FIG. 28, error signal 658 represents the sum of quantization errorand addressing error (whereas error signal 653 in FIG. 27 representsaddressing error only), and therefore the noise transfer function (NTF)of noise shaping loop 60 is applied to quantization noise and addressingnoise (as opposed to addressing noise only as in FIG. 27). As a result,input signal 70 can be reproduced more accurately and/or with a lowernumber of actuator elements than would be possible without quantizationnoise shaping.

FIG. 29 is a simplified block diagram of a further embodiment of theinvention. As in FIGS. 27 and 28, the apparatus includes a controller 50and actuator array 100, with the controller 50 featuring a noise shapingloop 60. Noise shaping is applied to quantization noise and addressingnoise. However, in contrast to FIG. 28 where a single loop filter isused for both types of noise, in FIG. 29 the two types of noise areprocessed separately. The adder 542 and inverter 541 together subtractthe quantized signal 640 from the quantizer's input signal 603, therebyproducing signal 642 which represents quantization error. This isfiltered by a first loop filter 543 to produce filtered quantizationnoise signal 643, which is added to input signal 600 by adder 535.Likewise, adder 552 and inverter 551 together subtract the actual numberof moving elements in the A-position, represented by signal 651, fromthe desired number of moving elements in the A-position represented bythe quantized signal 640, producing signal 652 which representsaddressing error. This is filtered by a second loop filter 553 toproduce a filtered addressing noise signal 653, which is added to theinput signal 600 along with the filtered quantization noise signal 643.

The characteristics of addressing noise may differ from those ofquantization noise in any or all of the following ways:

-   -   Addressing noise may have higher peak amplitudes than        quantization noise, which is limited to a narrow range of values        (typically ±0.5 least significant bits if the quantizer does not        use dithering, although the range may be wider with dither).    -   The spectra of the types of noise may differ. For example,        quantization noise may be shaped in the quantizer, by using        dither with a triangular probability function, as described with        reference to FIG. 14. This results in quantization noise energy        already being concentrated primarily at high frequencies in the        signal prior to entering the noise-shaping loop. This technique        well known in the art, e.g. in the field of delta-sigma data        converters. Applying the same technique to addressing noise may        make the addressing-noise shaping loop unstable as described        with reference to FIG. 27, and may therefore be undesirable.    -   As described with reference to FIG. 27, addressing noise may        exhibit a higher degree of correlation with the input signal 70        than quantization noise does, thus a loop filter with a short,        smooth impulse response may be provided to maintain loop        stability, as opposed to quantization noise where a longer, less        smooth impulse response may be provided.

The use of two separate loop filters 543 and 553, for quantization noiseand addressing noise respectively, makes it possible to combineaggressive quantization noise shaping, e.g. using a finite impulseresponse (FIR) filter with a relatively long impulse response for loopfilter 543, with more conservative shaping of addressing noise, e.g.using a FIR with a shorter impulse response for loop filter 553. Moregenerally, different NTFs can be implemented for each type of noise tosuit the needs of the application.

The individual addressing methods and apparatus shown and describedherein are particularly useful for arrays of double-sided electrostaticactuators. The noise reduction methods and apparatus shown and describedherein are useful in a wide variety of arrays such as but not limited tothe arrays shown and described herein.

Features of the present invention which are described in the context ofseparate embodiments may also be provided in combination in a singleembodiment. Conversely, features of the invention, including methodsteps, which are described for brevity in the context of a singleembodiment or in a certain order may be provided separately or in anysuitable subcombination or in a different order.

Any or all of computerized sensors, output devices or displays,processors, data storage and networks may be used as appropriate toimplement any of the methods and apparatus shown and described herein.

It is appreciated that terminology such as “mandatory”, “required”,“need” and “must” refer to implementation choices made within thecontext of a particular implementation or application describedherewithin for clarity and are not intended to be limiting since in analternative implementation, the same elements might be defined as notmandatory and not required or might even be eliminated altogether.

It is appreciated that software components of the present inventionincluding programs and data may, if desired, be implemented in ROM (readonly memory) form including CD-ROMs, EPROMs and EEPROMs, or may bestored in any other suitable typically non-transitory computer-readablemedium such as but not limited to disks of various kinds, cards ofvarious kinds and RAMs. Components described herein as software may,alternatively, be implemented wholly or partly in hardware, if desired,using conventional techniques. Conversely, components described hereinas hardware may, alternatively, be implemented wholly or partly insoftware, if desired, using conventional techniques.

Included in the scope of the present invention, inter alia, areelectromagnetic signals carrying computer-readable instructions forperforming any or all of the steps of any of the methods shown anddescribed herein, in any suitable order; machine-readable instructionsfor performing any or all of the steps of any of the methods shown anddescribed herein, in any suitable order; program storage devicesreadable by machine, tangibly embodying a program of instructionsexecutable by the machine to perform any or all of the steps of any ofthe methods shown and described herein, in any suitable order; acomputer program product comprising a computer useable medium havingcomputer readable program code, such as executable code, having embodiedtherein, and/or including computer readable program code for performing,any or all of the steps of any of the methods shown and describedherein, in any suitable order; any technical effects brought about byany or all of the steps of any of the methods shown and describedherein, when performed in any suitable order; any suitable apparatus ordevice or combination of such, programmed to perform, alone or incombination, any or all of the steps of any of the methods shown anddescribed herein, in any suitable order; electronic devices eachincluding a processor and a cooperating input device and/or outputdevice and operative to perform in software any steps shown anddescribed herein; information storage devices or physical records, suchas disks or hard drives, causing a computer or other device to beconfigured so as to carry out any or all of the steps of any of themethods shown and described herein, in any suitable order; a programpre-stored e.g. in memory or on an information network such as theInternet, before or after being downloaded, which embodies any or all ofthe steps of any of the methods shown and described herein, in anysuitable order, and the method of uploading or downloading such, and asystem including server/s and/or client/s for using such; and hardwarewhich performs any or all of the steps of any of the methods shown anddescribed herein, in any suitable order, either alone or in conjunctionwith software. Any computer-readable or machine-readable media describedherein is intended to include non-transitory computer- ormachine-readable media.

Any computations or other forms of analysis described herein may beperformed by a suitable computerized method. Any step described hereinmay be computer-implemented. The invention shown and described hereinmay include (a) using a computerized method to identify a solution toany of the problems or for any of the objectives described herein, thesolution optionally include at least one of a decision, an action, aproduct, a service or any other information described herein thatimpacts, in a positive manner, a problem or objectives described herein;and (b) outputting the solution.

The scope of the present invention is not limited to structures andfunctions specifically described herein and is also intended to includedevices which have the capacity to yield a structure, or perform afunction, described herein, such that even though users of the devicemay not use the capacity, they are if they so desire able to modify thedevice to obtain the structure or function.

Features of the present invention which are described in the context ofseparate embodiments may also be provided in combination in a singleembodiment.

Conversely, features of the invention, including method steps, which aredescribed for brevity in the context of a single embodiment or in acertain order may be provided separately or in any suitablesubcombination or in a different order. “e.g.” is used herein in thesense of a specific example which is not intended to be limiting.Devices, apparatus or systems shown coupled in any of the drawings mayin fact be integrated into a single platform in certain embodiments ormay be coupled via any appropriate wired or wireless coupling such asbut not limited to optical fiber, Ethernet, Wireless LAN, HomePNA, powerline communication, cell phone, PDA, Blackberry GPRS, Satelliteincluding GPS, or other mobile delivery. It is appreciated that in thedescription and drawings shown and described herein, functionalitiesdescribed or illustrated as systems and sub-units thereof can also beprovided as methods and steps therewithin, and functionalities describedor illustrated as methods and steps therewithin can also be provided assystems and sub-units thereof. The scale used to illustrate variouselements in the drawings is merely exemplary and/or appropriate forclarity of presentation and is not intended to be limiting.

The invention claimed is:
 1. Apparatus for generating a target physicaleffect, at least one attribute of which corresponds to at least onecharacteristic of a digital input signal sampled periodically, theapparatus comprising: a multiplicity of electrostatic actuator elements,each comprising a moving element moving between first and secondelectrodes, the multiplicity of electrostatic actuator elementsincluding Nr first subsets (R-subsets) of actuator elements and Ncsecond subsets (C-subsets) of actuator elements, wherein a firstpartitioning of the multiplicity of actuator elements yields the Nrfirst subsets (R-subsets) and a second partitioning of the multiplicityof actuator elements yields the Nc second subsets (C-subsets); a firstplurality of Nr electrical connections (R-wires) interconnecting themoving elements of actuator elements in each R-subset, such that themoving element of any actuator element in each individual R-subset iselectrically connected to the moving elements of all other actuatorelements in the individual R-subset, and electrically isolated from themoving elements of all actuator elements not in the individual R-subset;a second plurality of Nc electrical connections (A-wires)interconnecting the first electrodes of actuator elements in eachC-subset, such that the first electrode of any actuator element in eachindividual C-subset is electrically connected to the first electrode ofall other actuator elements in the individual C-subset, and electricallyisolated from all actuator elements not in the individual C-subset; athird plurality of Nc electrical connections (B-wires) interconnectingthe second electrodes of actuator elements in each C-subset, such thatthe second electrode of any actuator element in each individual C-subsetis electrically connected to the second electrode of all other actuatorelements in said individual C-subset, and electrically isolated from allactuator elements not in said individual C-subset; and a controllerelectrically connected to said first, second and third pluralities ofelectrical connections, operative to receive a digital input signal, andto apply one of a predetermined, finite set of electric potentials toeach of said electrical connections respectively, such that resultingmovements of said moving elements together produce the desired physicaleffect, wherein said controller is operative to determine, according tothe digital input signal, Nr-tuplets of electrical potential forapplication to said first plurality of Nr electrical connections(R-wires) respectively, first Nc-tuplets of electrical potential forapplication to said second plurality of Nc electrical connections(A-wires) respectively, and second Nc-tuplets of electrical potentialfor application to said third plurality of Nc electrical connections(B-wires) respectively.
 2. Apparatus according to claim 1, wherein saidNr-tuplets, first Nc-tuplets and second Nc-tuplets are determined bysaid controller such that their application to said first, second andthird plurality of electrical connections respectively causes the movingelements of said multiplicity of actuator elements to produce a physicaleffect which corresponds to at least one characteristic of the digitalinput signal.
 3. Apparatus according to claim 1, wherein intersectionsof any individual one of said first subsets of actuator elements and anyindividual one of said second subsets of actuator elements all include auniform number of actuator elements.
 4. Apparatus according to claim 1,wherein said predetermined, finite set of electric potentials includesfirst and second finite sets of electrical potential values and wherein:said Nr-tuplets of electrical potentials are selected from said firstfinite sets of electrical potential values; and said first and secondNc-tuplets of electrical potentials are selected from said second finitesets of electrical potential values.
 5. Apparatus according to claim 1,wherein said predetermined, finite set of electric potentials includesfirst and second finite sets of electrical potential values and wherein:said Nr-tuplets of electrical potentials are selected from said firstfinite sets of electrical potential values; and said first and secondNc-tuplets of electrical potentials are selected from said second finitesets of electrical potential values, where both of said first and secondfinite sets of electrical potential values have exactly two values. 6.Apparatus according to claim 1, wherein said controller is operative toperiodically apply one of the predetermined, finite sets of electricpotentials to each member of said first, second and third pluralities ofelectrical connections respectively.
 7. Apparatus according to claim 6,wherein said controller is operative to periodically determine,according to the digital input signal, Nr-tuplets of electricalpotential for periodic application to the Nr members of said firstplurality of electrical connections (R-wires) respectively, firstNc-tuplets of electrical potential for periodic application to the Ncmembers of said second plurality of electrical connections (A-wires)respectively, and second Nc-tuplets of electrical potential for periodicapplication to the Nc members of said third plurality of electricalconnections (B-wires) respectively; and wherein application of saidNr-tuplets, first Nc-tuplets and second Nc-tuplets of electricalpotential is synchronous with an actuation clock, such that an Nr-tupletof electrical potential is applied to said first plurality of Nrelectrical connections (R-wires), a first Nc-tuplet of electricalpotential is applied to said second plurality of Nc electricalconnections (R-wires), and a second Nc-tuplet of electrical potential isapplied to said third plurality of Nc electrical connections (B-wires),periodically and simultaneously, once every actuation clock cycle, forthe duration of said actuation clock cycle.
 8. Apparatus according to 7,wherein each moving element is operative, responsive to said potentialapplied by the controller, to move from a first extreme position, closerto said first electrode than to said second electrode, to a secondextreme position, closer to said second electrode than to said firstelectrode, and back, and where such movements are completed within kactuation clock cycle, where k is a positive integer.
 9. Apparatusaccording to claim 7, wherein each moving element is operative,responsive to potentials applied by the controller, to move from a firstextreme position, closer to said first electrode than to said secondelectrode, to a second extreme position, closer to said second electrodethan to said first electrode, and back, and wherein, once per actuationclock cycle, said controller is operative for computing a net_movesnumber characterized in that if, during that individual clock cycle, m1moving elements are released from said first extreme position and m2moving elements are released from said second extreme position, andm2−m1=net_moves, the physical effect is produced during the individualclock cycle.
 10. Apparatus according to claim 9, wherein said controlleris additionally operative to determine, once per clock cycle,application-effective electrical potentials which, when applied to saidfirst plurality of Nr electrical connections (R-wires), said secondplurality of Nc electrical connections (A-wires), and said thirdplurality of Nc electrical connections (B-wires) respectively, areoperative to effect: release of k1 moving elements from the firstextreme position release of k2 moving elements from the second extremeposition such that k1−k2 is close enough to net_moves to produce aphysical effect which resembles the target physical effect sufficientlyclosely for purposes of a given application.
 11. Apparatus according toclaim 10, wherein, during a single actuation clock cycle, some of saidmultiplicity of moving elements leave one of their extreme positions anddo not yet reach the other of their extreme positions and others of saidmultiplicity of moving elements reach one of their extreme positionshaving left the other of their extreme positions during an actuationclock cycle previous to said single actuation clock cycle and whereinsaid application-effective electrical potentials are selected by saidcontroller to ensure that any moving elements having been released,previously to said single actuation clock cycle, from one of theirextreme positions reach the opposite extreme position during anappropriate clock cycle.
 12. Apparatus according to claim 10, wherein:each R-subset includes Nc moving elements each C-subset includes Nrmoving elements R-wires are numbered 0 to Nr−1 A-wires and B-wires arenumbered 0 to Nc−1 moving elements are numbered such that each movingelement has the number: Nr×C-subset number+R-subset number. 13.Apparatus according to claim 12, wherein said controller selects saidapplication-effective electric potentials such that, at each actuationclock cycle, the numbers of all moving elements currently in theA-position form a continuous wraparound sequence, and the numbers of allmoving elements currently in the B-position also form a continuouswraparound sequence.
 14. Apparatus according to claim 12, wherein saidcontroller selects said application-effective electric potentials suchthat, at each actuation clock cycle, the numbers of all moving elementscurrently in the A-position form S continuous wraparound sequences, andthe numbers of all moving elements currently in the B-position also formS continuous wraparound sequences, where S is a positive integer. 15.Apparatus according to claim 12, wherein said controller generates, ateach actuation clock cycle: (i) Nr R-signals r0 to r(Nr−1) controllingthe potential applied to each of said R-wires R0 to R(Nr−1), (ii) NcA-signals a0 to a(Nc−1) controlling the potential applied to each ofsaid A-wires A0 to A(Nc−1), and (iii) Nc B-signals b0 to b(Nc−1)controlling the potential applied to each of said B-wires B0 to B(Nc−1);and wherein said controller changes the assignment of R-signals toR-wires and/or the assignment of A-signals to A-wires and B-signals toB-wires during operation of the apparatus.
 16. Apparatus according toclaim 12, wherein said controller generates, at each actuation clockcycle: (i) Nr R-signals r0 to r(Nr−1) controlling the potential appliedto each of said R-wires R0 to R(Nr−1), (ii) Nc A-signals a0 to a(Nc−1)controlling the potential applied to each of said A-wires A0 to A(Nc−1),and (iii) Nc B-signals b0 to b(Nc−1) controlling the potential appliedto each of said B-wires B0 to B(Nc−1); wherein said changes in theassignment of R-signals to R-wires and/or the assignment of A-signals toA-wires and B-signals to B-wires occur periodically.
 17. Apparatusaccording to claim 12, wherein said changes in the assignment ofR-signals to R-wires and/or the assignment of A-signals to A-wires andB-signals to B-wires shape the frequency spectrum of mismatch noiseresulting from differences in the magnitude of the physical effectproduced by each actuator element, such that the physical effectproduced by the apparatus as a whole more closely resembles the targetphysical effect.
 18. Apparatus according to claim 10, which suffers fromaddressing noise resulting from nonzero differences (addressing errors)between k1−k2 and net_moves during one or more actuation clock cycles,said addressing noise having a frequency spectrum, wherein saidcontroller includes an addressing noise shaping loop operative to shapesaid frequency spectrum of said addressing noise, such that addressingnoise energy is reduced within a frequency band of interest andincreased outside said band of interest.
 19. Apparatus according toclaim 10, which suffers from quantization noise resulting from thenumber of actuator elements in said actuator array being less than thenumber of possible values that the digital input signal can assume, saidquantization noise having a frequency spectrum, wherein said controllerincludes a quantization noise shaping loop operative to shape saidfrequency spectrum of said quantization noise, such that quantizationnoise energy is reduced within a frequency band of interest andincreased outside said band of interest.
 20. Apparatus according toclaim 10, which suffers from addressing noise resulting from nonzerodifferences (addressing errors) between k1−k2 and net_moves during oneor more actuation clock cycles, said addressing noise having anaddressing noise spectrum, and also suffers from quantization noiseresulting from the number of actuator elements in said actuator arraybeing less than the number of possible values that the digital inputsignal can assume, said quantization noise having a quantization noisespectrum, wherein said controller includes a noise shaping loopoperative to shape the frequency spectra of both of said addressingnoise and said quantization noise, such that both addressing noiseenergy and quantization noise energy are reduced within a frequency bandof interest and increased outside said band of interest, and whereinsaid noise shaping loop has a single loop filter having a single impulseresponse and receiving the sum of said addressing noise and saidquantization noise, such that the frequency spectra of both of saidaddressing noise and said quantization noise are shaped according to asingle noise transfer function determined by said single impulseresponse.
 21. Apparatus according to claim 10, which suffers fromaddressing noise resulting from nonzero differences (addressing errors)between k1−k2 and net_moves during one or more actuation clock cycles,said addressing noise having an addressing noise spectrum, and alsosuffers from quantization noise resulting from the number of actuatorelements in said actuator array being less than the number of possiblevalues that the digital input signal can assume, said quantization noisehaving a quantization noise spectrum; wherein said controller includes:a noise shaping loop operative to shape the frequency spectra of both ofsaid addressing noise and said quantization noise, such that bothaddressing noise energy and quantization noise energy are reduced withina frequency band of interest and increased outside said band ofinterest; and an addressing noise shaping loop operative to shape thefrequency spectrum of said addressing noise and a quantization noiseshaping loop operative to shape the frequency spectrum of saidquantization noise, such that both addressing noise energy andquantization noise energy are reduced within respective frequency bandsof interest and increased outside said bands of interest.
 22. Apparatusaccording to claim 1, wherein said controller includes a low-passfilter.
 23. Apparatus according to claim 1, wherein each moving elementis operative, responsive to potentials applied by the controller, tomove from a first extreme position closer to said first electrode thanto said second electrode, to a second extreme position closer to saidsecond electrode than to said first electrode, and back, wherein theabsence of any potentials applied to said first plurality of Nrelectrical connections, said second plurality of Nc electricalconnections, and said third plurality of Nc electrical connections, suchas for example, when the apparatus is powered down, said moving elementsreturn to a resting position located between said first and secondextreme positions, and wherein said controller additionally comprisesmeans to cause one or more of said moving elements to move from theirresting position to one of said first and second extreme positions. 24.A method for manufacturing apparatus for generating a physical effect,at least one attribute of which corresponds to at least onecharacteristic of a digital input signal sampled periodically, themethod comprising: providing a multiplicity of electrostatic actuatorelements, each comprising a moving element moving between first andsecond electrodes, said providing including defining: a firstpartitioning of said multiplicity of actuator elements into Nr firstsubsets (R-subsets), and a second partitioning of said multiplicity ofactuator elements into Nc second subsets (C-subsets); interconnectingthe moving elements of actuator elements in each R-subset, via a firstplurality of Nr electrical connections (R-wires), such that the movingelement of any actuator element in each individual R-subset iselectrically connected to the moving elements of all other actuatorelements in said individual R-subset, and electrically isolated from themoving elements of all actuator elements not in said individualR-subset; interconnecting the first electrodes of actuator elements ineach C-subset, via a second plurality of Nc electrical connections(A-wires), such that the first electrode of any actuator element in eachindividual C-subset is electrically connected to the first electrode ofall other actuator elements in said individual C-subset, andelectrically isolated from all actuator elements not in said individualC-subset; interconnecting the second electrodes of actuator elements ineach C-subset, a third plurality of Nc electrical connections (B-wires),such that the second electrode of any actuator element in eachindividual C-subset is electrically connected to the second electrode ofall other actuator elements in said individual C-subset, andelectrically isolated from all actuator elements not in said individualC-subset; and providing a controller electrically connected to saidfirst, second and third pluralities of electrical connections, operativeto receive a digital input signal, and to apply one of a predetermined,finite set of electric potentials to each of said electrical connectionsrespectively, such that resulting movements of said moving elementstogether produce the desired physical effect, wherein the controllerincludes a low-pass filter.
 25. A method according to claim 24, wheresaid controller includes a low-pass filter.
 26. A method for generatinga physical effect, at least one attribute of which corresponds to atleast one characteristic of a digital input signal sampled periodically,the method comprising: providing a multiplicity of electrostaticactuator elements, each comprising a moving element moving between firstand second electrodes, the multiplicity of electrostatic actuatorelements including Nr first subsets (R-subsets) of actuator elements andNc second subsets (C-subsets) of actuator elements, wherein a firstpartitioning of said multiplicity of actuator elements yields said Nrfirst subsets (R-subsets) and a second partitioning of said multiplicityof actuator elements yields said Nc second subsets (C-subsets);providing a first plurality of Nr electrical connections (R-wires)interconnecting the moving elements of actuator elements in eachR-subset, such that the moving element of any actuator element in eachindividual R-subset is electrically connected to the moving elements ofall other actuator elements in said individual R-subset, andelectrically isolated from the moving elements of all actuator elementsnot in said individual R-subset; providing a second plurality of Ncelectrical connections (A-wires) interconnecting the first electrodes ofactuator elements in each C-subset, such that the first electrode of anyactuator element in each individual C-subset is electrically connectedto the first electrode of all other actuator elements in said individualC-subset, and electrically isolated from all actuator elements not insaid individual C-subset; providing a third plurality of Nc electricalconnections (B-wires) interconnecting the second electrodes of actuatorelements in each C-subset, such that the second electrode of anyactuator element in each individual C-subset is electrically connectedto the second electrode of all other actuator elements in saidindividual C-subset, and electrically isolated from all actuatorelements not in said individual C-subset; and using a controller,electrically connected to said first, second and third pluralities ofelectrical connections, to receive a digital input signal, and to applyone of a predetermined, finite set of electric potentials to each ofsaid electrical connections respectively, such that resulting movementsof said moving elements together produce the desired physical effect.